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The netfilter code relies only on the implicit semantics of
local_bh_disable() for serializing wt_write_recseq sections. RT breaks
that and needs explicit serialization here.
Reported-by: Peter LaDow <petela@gocougs.wsu.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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in response to the oops in ip_output.c:ip_send_unicast_reply under high
network load with CONFIG_PREEMPT_RT_FULL=y, reported by Sami Pietikainen
<Sami.Pietikainen@wapice.com>, this patch adds local serialization in
ip_send_unicast_reply.
from ip_output.c:
/*
* Generic function to send a packet as reply to another packet.
* Used to send some TCP resets/acks so far.
*
* Use a fake percpu inet socket to avoid false sharing and contention.
*/
static DEFINE_PER_CPU(struct inet_sock, unicast_sock) = {
...
which was added in commit be9f4a44 in linux-stable. The git log, wich
introduced the PER_CPU unicast_sock, states:
<snip>
commit be9f4a44e7d41cee50ddb5f038fc2391cbbb4046
Author: Eric Dumazet <edumazet@google.com>
Date: Thu Jul 19 07:34:03 2012 +0000
ipv4: tcp: remove per net tcp_sock
tcp_v4_send_reset() and tcp_v4_send_ack() use a single socket
per network namespace.
This leads to bad behavior on multiqueue NICS, because many cpus
contend for the socket lock and once socket lock is acquired, extra
false sharing on various socket fields slow down the operations.
To better resist to attacks, we use a percpu socket. Each cpu can
run without contention, using appropriate memory (local node)
<snip>
The per-cpu here thus is assuming exclusivity serializing per cpu - so
the use of get_cpu_ligh introduced in
net-use-cpu-light-in-ip-send-unicast-reply.patch, which droped the
preempt_disable in favor of a migrate_disable is probably wrong as this
only handles the referencial consistency but not the serialization. To
evade a preempt_disable here a local lock would be needed.
Therapie:
* add local lock:
* and re-introduce local serialization:
Tested on x86 with high network load using the testcase from Sami Pietikainen
while : ; do wget -O - ftp://LOCAL_SERVER/empty_file > /dev/null 2>&1; done
Link: http://www.spinics.net/lists/linux-rt-users/msg11007.html
Cc: stable-rt@vger.kernel.org
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Replace it by a local lock. Though that's pretty inefficient :(
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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1)enqueue_to_backlog() (called from netif_rx) should be
bind to a particluar CPU. This can be achieved by
disabling migration. No need to disable preemption
2)Fixes crash "BUG: scheduling while atomic: ksoftirqd"
in case of RT.
If preemption is disabled, enqueue_to_backog() is called
in atomic context. And if backlog exceeds its count,
kfree_skb() is called. But in RT, kfree_skb() might
gets scheduled out, so it expects non atomic context.
3)When CONFIG_PREEMPT_RT_FULL is not defined,
migrate_enable(), migrate_disable() maps to
preempt_enable() and preempt_disable(), so no
change in functionality in case of non-RT.
-Replace preempt_enable(), preempt_disable() with
migrate_enable(), migrate_disable() respectively
-Replace get_cpu(), put_cpu() with get_cpu_light(),
put_cpu_light() respectively
Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Acked-by: Rajan Srivastava <Rajan.Srivastava@freescale.com>
Cc: <rostedt@goodmis.orgn>
Link: http://lkml.kernel.org/r/1337227511-2271-1-git-send-email-Priyanka.Jain@freescale.com
Cc: stable-rt@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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There are (probably rare) situations when a system crashed and the system
console becomes unresponsive but the network icmp layer still is alive.
Wouldn't it be wonderful, if we then could submit a sysreq command via ping?
This patch provides this facility. Please consult the updated documentation
Documentation/sysrq.txt for details.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
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qdisc_lock is taken w/o disabling interrupts or bottom halfs. So code
holding a qdisc_lock() can be interrupted and softirqs can run on the
return of interrupt in !RT.
The spin_trylock() in net_tx_action() makes sure, that the softirq
does not deadlock. When the lock can't be acquired q is requeued and
the NET_TX softirq is raised. That causes the softirq to run over and
over.
That works in mainline as do_softirq() has a retry loop limit and
leaves the softirq processing in the interrupt return path and
schedules ksoftirqd. The task which holds qdisc_lock cannot be
preempted, so the lock is released and either ksoftirqd or the next
softirq in the return from interrupt path can proceed. Though it's a
bit strange to actually run MAX_SOFTIRQ_RESTART (10) loops before it
decides to bail out even if it's clear in the first iteration :)
On RT all softirq processing is done in a FIFO thread and we don't
have a loop limit, so ksoftirqd preempts the lock holder forever and
unqueues and requeues until the reset button is hit.
Due to the forced threading of ksoftirqd on RT we actually cannot
deadlock on qdisc_lock because it's a "sleeping lock". So it's safe to
replace the spin_trylock() with a spin_lock(). When contended,
ksoftirqd is scheduled out and the lock holder can proceed.
[ tglx: Massaged changelog and code comments ]
Solved-by: Thomas Gleixner <tglx@linuxtronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Carsten Emde <cbe@osadl.org>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Claudio R. Goncalves <lclaudio@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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for outstanding qdisc_run calls
On PREEMPT_RT enabled systems the interrupt handler run as threads at prio 50
(by default). If a high priority userspace process tries to shut down a busy
network interface it might spin in a yield loop waiting for the device to
become idle. With the interrupt thread having a lower priority than the
looping process it might never be scheduled and so result in a deadlock on UP
systems.
With Magic SysRq the following backtrace can be produced:
> test_app R running 0 174 168 0x00000000
> [<c02c7070>] (__schedule+0x220/0x3fc) from [<c02c7870>] (preempt_schedule_irq+0x48/0x80)
> [<c02c7870>] (preempt_schedule_irq+0x48/0x80) from [<c0008fa8>] (svc_preempt+0x8/0x20)
> [<c0008fa8>] (svc_preempt+0x8/0x20) from [<c001a984>] (local_bh_enable+0x18/0x88)
> [<c001a984>] (local_bh_enable+0x18/0x88) from [<c025316c>] (dev_deactivate_many+0x220/0x264)
> [<c025316c>] (dev_deactivate_many+0x220/0x264) from [<c023be04>] (__dev_close_many+0x64/0xd4)
> [<c023be04>] (__dev_close_many+0x64/0xd4) from [<c023be9c>] (__dev_close+0x28/0x3c)
> [<c023be9c>] (__dev_close+0x28/0x3c) from [<c023f7f0>] (__dev_change_flags+0x88/0x130)
> [<c023f7f0>] (__dev_change_flags+0x88/0x130) from [<c023f904>] (dev_change_flags+0x10/0x48)
> [<c023f904>] (dev_change_flags+0x10/0x48) from [<c024c140>] (do_setlink+0x370/0x7ec)
> [<c024c140>] (do_setlink+0x370/0x7ec) from [<c024d2f0>] (rtnl_newlink+0x2b4/0x450)
> [<c024d2f0>] (rtnl_newlink+0x2b4/0x450) from [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4)
> [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4) from [<c0256740>] (netlink_rcv_skb+0xac/0xc0)
> [<c0256740>] (netlink_rcv_skb+0xac/0xc0) from [<c024bbd8>] (rtnetlink_rcv+0x18/0x24)
> [<c024bbd8>] (rtnetlink_rcv+0x18/0x24) from [<c02561b8>] (netlink_unicast+0x13c/0x198)
> [<c02561b8>] (netlink_unicast+0x13c/0x198) from [<c025651c>] (netlink_sendmsg+0x264/0x2e0)
> [<c025651c>] (netlink_sendmsg+0x264/0x2e0) from [<c022af98>] (sock_sendmsg+0x78/0x98)
> [<c022af98>] (sock_sendmsg+0x78/0x98) from [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278)
> [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278) from [<c022cf08>] (__sys_sendmsg+0x48/0x78)
> [<c022cf08>] (__sys_sendmsg+0x48/0x78) from [<c0009320>] (ret_fast_syscall+0x0/0x2c)
This patch works around the problem by replacing yield() by msleep(1), giving
the interrupt thread time to finish, similar to other changes contained in the
rt patch set. Using wait_for_completion() instead would probably be a better
solution.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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=======================================================
[ INFO: possible circular locking dependency detected ]
3.0.0-rc3+ #26
-------------------------------------------------------
ip/1104 is trying to acquire lock:
(local_softirq_lock){+.+...}, at: [<ffffffff81056d12>] __local_lock+0x25/0x68
but task is already holding lock:
(sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (sk_lock-AF_INET){+.+...}:
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff813e2781>] lock_sock_nested+0x82/0x92
[<ffffffff81433308>] lock_sock+0x10/0x12
[<ffffffff81433afa>] tcp_close+0x1b/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
-> #0 (local_softirq_lock){+.+...}:
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
*** DEADLOCK ***
1 lock held by ip/1104:
#0: (sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
stack backtrace:
Pid: 1104, comm: ip Not tainted 3.0.0-rc3+ #26
Call Trace:
[<ffffffff81081649>] print_circular_bug+0x1f8/0x209
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c75>] ? get_parent_ip+0x11/0x41
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c8c>] ? get_parent_ip+0x28/0x41
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff81433308>] ? lock_sock+0x10/0x12
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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raise_softirq_irqoff() disables interrupts and wakes the softirq
daemon, but after reenabling interrupts there is no preemption check,
so the execution of the softirq thread might be delayed arbitrarily.
In principle we could add that check to local_irq_enable/restore, but
that's overkill as the rasie_softirq_irqoff() sections are the only
ones which show this behaviour.
Reported-by: Carsten Emde <cbe@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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On RT write_seqcount_begin() disables preemption and device_rename()
allocates memory with GFP_KERNEL and grabs later the sysfs_mutex
mutex. Serialize with a mutex and add use the non preemption disabling
__write_seqcount_begin().
To avoid writer starvation, let the reader grab the mutex and release
it when it detects a writer in progress. This keeps the normal case
(no reader on the fly) fast.
[ tglx: Instead of replacing the seqcount by a mutex, add the mutex ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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This code triggers the new WARN in __raise_softirq_irqsoff() though it
actually looks at the softirq pending bit and calls into the softirq
code, but that fits not well with the context related softirq model of
RT. It's correct on mainline though, but going through
local_bh_disable/enable here is not going to hurt badly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The netfilter code relies only on the implicit semantics of
local_bh_disable() for serializing wt_write_recseq sections. RT breaks
that and needs explicit serialization here.
Reported-by: Peter LaDow <petela@gocougs.wsu.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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in response to the oops in ip_output.c:ip_send_unicast_reply under high
network load with CONFIG_PREEMPT_RT_FULL=y, reported by Sami Pietikainen
<Sami.Pietikainen@wapice.com>, this patch adds local serialization in
ip_send_unicast_reply.
from ip_output.c:
/*
* Generic function to send a packet as reply to another packet.
* Used to send some TCP resets/acks so far.
*
* Use a fake percpu inet socket to avoid false sharing and contention.
*/
static DEFINE_PER_CPU(struct inet_sock, unicast_sock) = {
...
which was added in commit be9f4a44 in linux-stable. The git log, wich
introduced the PER_CPU unicast_sock, states:
<snip>
commit be9f4a44e7d41cee50ddb5f038fc2391cbbb4046
Author: Eric Dumazet <edumazet@google.com>
Date: Thu Jul 19 07:34:03 2012 +0000
ipv4: tcp: remove per net tcp_sock
tcp_v4_send_reset() and tcp_v4_send_ack() use a single socket
per network namespace.
This leads to bad behavior on multiqueue NICS, because many cpus
contend for the socket lock and once socket lock is acquired, extra
false sharing on various socket fields slow down the operations.
To better resist to attacks, we use a percpu socket. Each cpu can
run without contention, using appropriate memory (local node)
<snip>
The per-cpu here thus is assuming exclusivity serializing per cpu - so
the use of get_cpu_ligh introduced in
net-use-cpu-light-in-ip-send-unicast-reply.patch, which droped the
preempt_disable in favor of a migrate_disable is probably wrong as this
only handles the referencial consistency but not the serialization. To
evade a preempt_disable here a local lock would be needed.
Therapie:
* add local lock:
* and re-introduce local serialization:
Tested on x86 with high network load using the testcase from Sami Pietikainen
while : ; do wget -O - ftp://LOCAL_SERVER/empty_file > /dev/null 2>&1; done
Link: http://www.spinics.net/lists/linux-rt-users/msg11007.html
Cc: stable-rt@vger.kernel.org
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Replace it by a local lock. Though that's pretty inefficient :(
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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1)enqueue_to_backlog() (called from netif_rx) should be
bind to a particluar CPU. This can be achieved by
disabling migration. No need to disable preemption
2)Fixes crash "BUG: scheduling while atomic: ksoftirqd"
in case of RT.
If preemption is disabled, enqueue_to_backog() is called
in atomic context. And if backlog exceeds its count,
kfree_skb() is called. But in RT, kfree_skb() might
gets scheduled out, so it expects non atomic context.
3)When CONFIG_PREEMPT_RT_FULL is not defined,
migrate_enable(), migrate_disable() maps to
preempt_enable() and preempt_disable(), so no
change in functionality in case of non-RT.
-Replace preempt_enable(), preempt_disable() with
migrate_enable(), migrate_disable() respectively
-Replace get_cpu(), put_cpu() with get_cpu_light(),
put_cpu_light() respectively
Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Acked-by: Rajan Srivastava <Rajan.Srivastava@freescale.com>
Cc: <rostedt@goodmis.orgn>
Link: http://lkml.kernel.org/r/1337227511-2271-1-git-send-email-Priyanka.Jain@freescale.com
Cc: stable-rt@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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There are (probably rare) situations when a system crashed and the system
console becomes unresponsive but the network icmp layer still is alive.
Wouldn't it be wonderful, if we then could submit a sysreq command via ping?
This patch provides this facility. Please consult the updated documentation
Documentation/sysrq.txt for details.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
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qdisc_lock is taken w/o disabling interrupts or bottom halfs. So code
holding a qdisc_lock() can be interrupted and softirqs can run on the
return of interrupt in !RT.
The spin_trylock() in net_tx_action() makes sure, that the softirq
does not deadlock. When the lock can't be acquired q is requeued and
the NET_TX softirq is raised. That causes the softirq to run over and
over.
That works in mainline as do_softirq() has a retry loop limit and
leaves the softirq processing in the interrupt return path and
schedules ksoftirqd. The task which holds qdisc_lock cannot be
preempted, so the lock is released and either ksoftirqd or the next
softirq in the return from interrupt path can proceed. Though it's a
bit strange to actually run MAX_SOFTIRQ_RESTART (10) loops before it
decides to bail out even if it's clear in the first iteration :)
On RT all softirq processing is done in a FIFO thread and we don't
have a loop limit, so ksoftirqd preempts the lock holder forever and
unqueues and requeues until the reset button is hit.
Due to the forced threading of ksoftirqd on RT we actually cannot
deadlock on qdisc_lock because it's a "sleeping lock". So it's safe to
replace the spin_trylock() with a spin_lock(). When contended,
ksoftirqd is scheduled out and the lock holder can proceed.
[ tglx: Massaged changelog and code comments ]
Solved-by: Thomas Gleixner <tglx@linuxtronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Carsten Emde <cbe@osadl.org>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Claudio R. Goncalves <lclaudio@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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for outstanding qdisc_run calls
On PREEMPT_RT enabled systems the interrupt handler run as threads at prio 50
(by default). If a high priority userspace process tries to shut down a busy
network interface it might spin in a yield loop waiting for the device to
become idle. With the interrupt thread having a lower priority than the
looping process it might never be scheduled and so result in a deadlock on UP
systems.
With Magic SysRq the following backtrace can be produced:
> test_app R running 0 174 168 0x00000000
> [<c02c7070>] (__schedule+0x220/0x3fc) from [<c02c7870>] (preempt_schedule_irq+0x48/0x80)
> [<c02c7870>] (preempt_schedule_irq+0x48/0x80) from [<c0008fa8>] (svc_preempt+0x8/0x20)
> [<c0008fa8>] (svc_preempt+0x8/0x20) from [<c001a984>] (local_bh_enable+0x18/0x88)
> [<c001a984>] (local_bh_enable+0x18/0x88) from [<c025316c>] (dev_deactivate_many+0x220/0x264)
> [<c025316c>] (dev_deactivate_many+0x220/0x264) from [<c023be04>] (__dev_close_many+0x64/0xd4)
> [<c023be04>] (__dev_close_many+0x64/0xd4) from [<c023be9c>] (__dev_close+0x28/0x3c)
> [<c023be9c>] (__dev_close+0x28/0x3c) from [<c023f7f0>] (__dev_change_flags+0x88/0x130)
> [<c023f7f0>] (__dev_change_flags+0x88/0x130) from [<c023f904>] (dev_change_flags+0x10/0x48)
> [<c023f904>] (dev_change_flags+0x10/0x48) from [<c024c140>] (do_setlink+0x370/0x7ec)
> [<c024c140>] (do_setlink+0x370/0x7ec) from [<c024d2f0>] (rtnl_newlink+0x2b4/0x450)
> [<c024d2f0>] (rtnl_newlink+0x2b4/0x450) from [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4)
> [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4) from [<c0256740>] (netlink_rcv_skb+0xac/0xc0)
> [<c0256740>] (netlink_rcv_skb+0xac/0xc0) from [<c024bbd8>] (rtnetlink_rcv+0x18/0x24)
> [<c024bbd8>] (rtnetlink_rcv+0x18/0x24) from [<c02561b8>] (netlink_unicast+0x13c/0x198)
> [<c02561b8>] (netlink_unicast+0x13c/0x198) from [<c025651c>] (netlink_sendmsg+0x264/0x2e0)
> [<c025651c>] (netlink_sendmsg+0x264/0x2e0) from [<c022af98>] (sock_sendmsg+0x78/0x98)
> [<c022af98>] (sock_sendmsg+0x78/0x98) from [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278)
> [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278) from [<c022cf08>] (__sys_sendmsg+0x48/0x78)
> [<c022cf08>] (__sys_sendmsg+0x48/0x78) from [<c0009320>] (ret_fast_syscall+0x0/0x2c)
This patch works around the problem by replacing yield() by msleep(1), giving
the interrupt thread time to finish, similar to other changes contained in the
rt patch set. Using wait_for_completion() instead would probably be a better
solution.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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=======================================================
[ INFO: possible circular locking dependency detected ]
3.0.0-rc3+ #26
-------------------------------------------------------
ip/1104 is trying to acquire lock:
(local_softirq_lock){+.+...}, at: [<ffffffff81056d12>] __local_lock+0x25/0x68
but task is already holding lock:
(sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (sk_lock-AF_INET){+.+...}:
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff813e2781>] lock_sock_nested+0x82/0x92
[<ffffffff81433308>] lock_sock+0x10/0x12
[<ffffffff81433afa>] tcp_close+0x1b/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
-> #0 (local_softirq_lock){+.+...}:
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
*** DEADLOCK ***
1 lock held by ip/1104:
#0: (sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
stack backtrace:
Pid: 1104, comm: ip Not tainted 3.0.0-rc3+ #26
Call Trace:
[<ffffffff81081649>] print_circular_bug+0x1f8/0x209
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c75>] ? get_parent_ip+0x11/0x41
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c8c>] ? get_parent_ip+0x28/0x41
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff81433308>] ? lock_sock+0x10/0x12
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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raise_softirq_irqoff() disables interrupts and wakes the softirq
daemon, but after reenabling interrupts there is no preemption check,
so the execution of the softirq thread might be delayed arbitrarily.
In principle we could add that check to local_irq_enable/restore, but
that's overkill as the rasie_softirq_irqoff() sections are the only
ones which show this behaviour.
Reported-by: Carsten Emde <cbe@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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On RT write_seqcount_begin() disables preemption and device_rename()
allocates memory with GFP_KERNEL and grabs later the sysfs_mutex
mutex. Serialize with a mutex and add use the non preemption disabling
__write_seqcount_begin().
To avoid writer starvation, let the reader grab the mutex and release
it when it detects a writer in progress. This keeps the normal case
(no reader on the fly) fast.
[ tglx: Instead of replacing the seqcount by a mutex, add the mutex ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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This code triggers the new WARN in __raise_softirq_irqsoff() though it
actually looks at the softirq pending bit and calls into the softirq
code, but that fits not well with the context related softirq model of
RT. It's correct on mainline though, but going through
local_bh_disable/enable here is not going to hurt badly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The netfilter code relies only on the implicit semantics of
local_bh_disable() for serializing wt_write_recseq sections. RT breaks
that and needs explicit serialization here.
Reported-by: Peter LaDow <petela@gocougs.wsu.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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in response to the oops in ip_output.c:ip_send_unicast_reply under high
network load with CONFIG_PREEMPT_RT_FULL=y, reported by Sami Pietikainen
<Sami.Pietikainen@wapice.com>, this patch adds local serialization in
ip_send_unicast_reply.
from ip_output.c:
/*
* Generic function to send a packet as reply to another packet.
* Used to send some TCP resets/acks so far.
*
* Use a fake percpu inet socket to avoid false sharing and contention.
*/
static DEFINE_PER_CPU(struct inet_sock, unicast_sock) = {
...
which was added in commit be9f4a44 in linux-stable. The git log, wich
introduced the PER_CPU unicast_sock, states:
<snip>
commit be9f4a44e7d41cee50ddb5f038fc2391cbbb4046
Author: Eric Dumazet <edumazet@google.com>
Date: Thu Jul 19 07:34:03 2012 +0000
ipv4: tcp: remove per net tcp_sock
tcp_v4_send_reset() and tcp_v4_send_ack() use a single socket
per network namespace.
This leads to bad behavior on multiqueue NICS, because many cpus
contend for the socket lock and once socket lock is acquired, extra
false sharing on various socket fields slow down the operations.
To better resist to attacks, we use a percpu socket. Each cpu can
run without contention, using appropriate memory (local node)
<snip>
The per-cpu here thus is assuming exclusivity serializing per cpu - so
the use of get_cpu_ligh introduced in
net-use-cpu-light-in-ip-send-unicast-reply.patch, which droped the
preempt_disable in favor of a migrate_disable is probably wrong as this
only handles the referencial consistency but not the serialization. To
evade a preempt_disable here a local lock would be needed.
Therapie:
* add local lock:
* and re-introduce local serialization:
Tested on x86 with high network load using the testcase from Sami Pietikainen
while : ; do wget -O - ftp://LOCAL_SERVER/empty_file > /dev/null 2>&1; done
Link: http://www.spinics.net/lists/linux-rt-users/msg11007.html
Cc: stable-rt@vger.kernel.org
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Replace it by a local lock. Though that's pretty inefficient :(
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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1)enqueue_to_backlog() (called from netif_rx) should be
bind to a particluar CPU. This can be achieved by
disabling migration. No need to disable preemption
2)Fixes crash "BUG: scheduling while atomic: ksoftirqd"
in case of RT.
If preemption is disabled, enqueue_to_backog() is called
in atomic context. And if backlog exceeds its count,
kfree_skb() is called. But in RT, kfree_skb() might
gets scheduled out, so it expects non atomic context.
3)When CONFIG_PREEMPT_RT_FULL is not defined,
migrate_enable(), migrate_disable() maps to
preempt_enable() and preempt_disable(), so no
change in functionality in case of non-RT.
-Replace preempt_enable(), preempt_disable() with
migrate_enable(), migrate_disable() respectively
-Replace get_cpu(), put_cpu() with get_cpu_light(),
put_cpu_light() respectively
Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Acked-by: Rajan Srivastava <Rajan.Srivastava@freescale.com>
Cc: <rostedt@goodmis.orgn>
Link: http://lkml.kernel.org/r/1337227511-2271-1-git-send-email-Priyanka.Jain@freescale.com
Cc: stable-rt@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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There are (probably rare) situations when a system crashed and the system
console becomes unresponsive but the network icmp layer still is alive.
Wouldn't it be wonderful, if we then could submit a sysreq command via ping?
This patch provides this facility. Please consult the updated documentation
Documentation/sysrq.txt for details.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
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qdisc_lock is taken w/o disabling interrupts or bottom halfs. So code
holding a qdisc_lock() can be interrupted and softirqs can run on the
return of interrupt in !RT.
The spin_trylock() in net_tx_action() makes sure, that the softirq
does not deadlock. When the lock can't be acquired q is requeued and
the NET_TX softirq is raised. That causes the softirq to run over and
over.
That works in mainline as do_softirq() has a retry loop limit and
leaves the softirq processing in the interrupt return path and
schedules ksoftirqd. The task which holds qdisc_lock cannot be
preempted, so the lock is released and either ksoftirqd or the next
softirq in the return from interrupt path can proceed. Though it's a
bit strange to actually run MAX_SOFTIRQ_RESTART (10) loops before it
decides to bail out even if it's clear in the first iteration :)
On RT all softirq processing is done in a FIFO thread and we don't
have a loop limit, so ksoftirqd preempts the lock holder forever and
unqueues and requeues until the reset button is hit.
Due to the forced threading of ksoftirqd on RT we actually cannot
deadlock on qdisc_lock because it's a "sleeping lock". So it's safe to
replace the spin_trylock() with a spin_lock(). When contended,
ksoftirqd is scheduled out and the lock holder can proceed.
[ tglx: Massaged changelog and code comments ]
Solved-by: Thomas Gleixner <tglx@linuxtronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Carsten Emde <cbe@osadl.org>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Claudio R. Goncalves <lclaudio@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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for outstanding qdisc_run calls
On PREEMPT_RT enabled systems the interrupt handler run as threads at prio 50
(by default). If a high priority userspace process tries to shut down a busy
network interface it might spin in a yield loop waiting for the device to
become idle. With the interrupt thread having a lower priority than the
looping process it might never be scheduled and so result in a deadlock on UP
systems.
With Magic SysRq the following backtrace can be produced:
> test_app R running 0 174 168 0x00000000
> [<c02c7070>] (__schedule+0x220/0x3fc) from [<c02c7870>] (preempt_schedule_irq+0x48/0x80)
> [<c02c7870>] (preempt_schedule_irq+0x48/0x80) from [<c0008fa8>] (svc_preempt+0x8/0x20)
> [<c0008fa8>] (svc_preempt+0x8/0x20) from [<c001a984>] (local_bh_enable+0x18/0x88)
> [<c001a984>] (local_bh_enable+0x18/0x88) from [<c025316c>] (dev_deactivate_many+0x220/0x264)
> [<c025316c>] (dev_deactivate_many+0x220/0x264) from [<c023be04>] (__dev_close_many+0x64/0xd4)
> [<c023be04>] (__dev_close_many+0x64/0xd4) from [<c023be9c>] (__dev_close+0x28/0x3c)
> [<c023be9c>] (__dev_close+0x28/0x3c) from [<c023f7f0>] (__dev_change_flags+0x88/0x130)
> [<c023f7f0>] (__dev_change_flags+0x88/0x130) from [<c023f904>] (dev_change_flags+0x10/0x48)
> [<c023f904>] (dev_change_flags+0x10/0x48) from [<c024c140>] (do_setlink+0x370/0x7ec)
> [<c024c140>] (do_setlink+0x370/0x7ec) from [<c024d2f0>] (rtnl_newlink+0x2b4/0x450)
> [<c024d2f0>] (rtnl_newlink+0x2b4/0x450) from [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4)
> [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4) from [<c0256740>] (netlink_rcv_skb+0xac/0xc0)
> [<c0256740>] (netlink_rcv_skb+0xac/0xc0) from [<c024bbd8>] (rtnetlink_rcv+0x18/0x24)
> [<c024bbd8>] (rtnetlink_rcv+0x18/0x24) from [<c02561b8>] (netlink_unicast+0x13c/0x198)
> [<c02561b8>] (netlink_unicast+0x13c/0x198) from [<c025651c>] (netlink_sendmsg+0x264/0x2e0)
> [<c025651c>] (netlink_sendmsg+0x264/0x2e0) from [<c022af98>] (sock_sendmsg+0x78/0x98)
> [<c022af98>] (sock_sendmsg+0x78/0x98) from [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278)
> [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278) from [<c022cf08>] (__sys_sendmsg+0x48/0x78)
> [<c022cf08>] (__sys_sendmsg+0x48/0x78) from [<c0009320>] (ret_fast_syscall+0x0/0x2c)
This patch works around the problem by replacing yield() by msleep(1), giving
the interrupt thread time to finish, similar to other changes contained in the
rt patch set. Using wait_for_completion() instead would probably be a better
solution.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
=======================================================
[ INFO: possible circular locking dependency detected ]
3.0.0-rc3+ #26
-------------------------------------------------------
ip/1104 is trying to acquire lock:
(local_softirq_lock){+.+...}, at: [<ffffffff81056d12>] __local_lock+0x25/0x68
but task is already holding lock:
(sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (sk_lock-AF_INET){+.+...}:
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff813e2781>] lock_sock_nested+0x82/0x92
[<ffffffff81433308>] lock_sock+0x10/0x12
[<ffffffff81433afa>] tcp_close+0x1b/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
-> #0 (local_softirq_lock){+.+...}:
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
lock(sk_lock-AF_INET);
lock(local_softirq_lock);
*** DEADLOCK ***
1 lock held by ip/1104:
#0: (sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12
stack backtrace:
Pid: 1104, comm: ip Not tainted 3.0.0-rc3+ #26
Call Trace:
[<ffffffff81081649>] print_circular_bug+0x1f8/0x209
[<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff810836e5>] lock_acquire+0x103/0x12e
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c75>] ? get_parent_ip+0x11/0x41
[<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81056d12>] ? __local_lock+0x25/0x68
[<ffffffff81046c8c>] ? get_parent_ip+0x28/0x41
[<ffffffff81056d12>] __local_lock+0x25/0x68
[<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
[<ffffffff81433308>] ? lock_sock+0x10/0x12
[<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
[<ffffffff81433c38>] tcp_close+0x159/0x355
[<ffffffff81453c99>] inet_release+0xc3/0xcd
[<ffffffff813dff3f>] sock_release+0x1f/0x74
[<ffffffff813dffbb>] sock_close+0x27/0x2b
[<ffffffff81129c63>] fput+0x11d/0x1e3
[<ffffffff81126577>] filp_close+0x70/0x7b
[<ffffffff8112667a>] sys_close+0xf8/0x13d
[<ffffffff814ae882>] system_call_fastpath+0x16/0x1b
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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