diff options
author | Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com> | 2015-12-14 10:19:11 (GMT) |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2015-12-19 10:07:01 (GMT) |
commit | 7bbee5ca3896f69f09c68be549cb8997abe6bca6 (patch) | |
tree | aa2ffe78b5f70617f6fec0da5d3075962bf392d2 /kernel | |
parent | 58c5661f2144c089bbc2e5d87c9ec1dc1d2964fe (diff) | |
download | linux-7bbee5ca3896f69f09c68be549cb8997abe6bca6.tar.xz |
kexec: Fix race between panic() and crash_kexec()
Currently, panic() and crash_kexec() can be called at the same time.
For example (x86 case):
CPU 0:
oops_end()
crash_kexec()
mutex_trylock() // acquired
nmi_shootdown_cpus() // stop other CPUs
CPU 1:
panic()
crash_kexec()
mutex_trylock() // failed to acquire
smp_send_stop() // stop other CPUs
infinite loop
If CPU 1 calls smp_send_stop() before nmi_shootdown_cpus(), kdump
fails.
In another case:
CPU 0:
oops_end()
crash_kexec()
mutex_trylock() // acquired
<NMI>
io_check_error()
panic()
crash_kexec()
mutex_trylock() // failed to acquire
infinite loop
Clearly, this is an undesirable result.
To fix this problem, this patch changes crash_kexec() to exclude others
by using the panic_cpu atomic.
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: kexec@lists.infradead.org
Cc: linux-doc@vger.kernel.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Minfei Huang <mnfhuang@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/20151210014630.25437.94161.stgit@softrs
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/kexec_core.c | 30 | ||||
-rw-r--r-- | kernel/panic.c | 8 |
2 files changed, 35 insertions, 3 deletions
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 11b64a6..c823f30 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -853,7 +853,12 @@ struct kimage *kexec_image; struct kimage *kexec_crash_image; int kexec_load_disabled; -void crash_kexec(struct pt_regs *regs) +/* + * No panic_cpu check version of crash_kexec(). This function is called + * only when panic_cpu holds the current CPU number; this is the only CPU + * which processes crash_kexec routines. + */ +void __crash_kexec(struct pt_regs *regs) { /* Take the kexec_mutex here to prevent sys_kexec_load * running on one cpu from replacing the crash kernel @@ -876,6 +881,29 @@ void crash_kexec(struct pt_regs *regs) } } +void crash_kexec(struct pt_regs *regs) +{ + int old_cpu, this_cpu; + + /* + * Only one CPU is allowed to execute the crash_kexec() code as with + * panic(). Otherwise parallel calls of panic() and crash_kexec() + * may stop each other. To exclude them, we use panic_cpu here too. + */ + this_cpu = raw_smp_processor_id(); + old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); + if (old_cpu == PANIC_CPU_INVALID) { + /* This is the 1st CPU which comes here, so go ahead. */ + __crash_kexec(regs); + + /* + * Reset panic_cpu to allow another panic()/crash_kexec() + * call. + */ + atomic_set(&panic_cpu, PANIC_CPU_INVALID); + } +} + size_t crash_get_memory_size(void) { size_t size = 0; diff --git a/kernel/panic.c b/kernel/panic.c index 06f31b49..b333380 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -136,9 +136,11 @@ void panic(const char *fmt, ...) * everything else. * If we want to run this after calling panic_notifiers, pass * the "crash_kexec_post_notifiers" option to the kernel. + * + * Bypass the panic_cpu check and call __crash_kexec directly. */ if (!crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); /* * Note smp_send_stop is the usual smp shutdown function, which @@ -161,9 +163,11 @@ void panic(const char *fmt, ...) * panic_notifiers and dumping kmsg before kdump. * Note: since some panic_notifiers can make crashed kernel * more unstable, it can increase risks of the kdump failure too. + * + * Bypass the panic_cpu check and call __crash_kexec directly. */ if (crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); bust_spinlocks(0); |