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author | Miklos Szeredi <miklos@szeredi.hu> | 2012-01-10 17:22:25 (GMT) |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2012-01-10 18:06:32 (GMT) |
commit | eaf5f9073533cde21c7121c136f1c3f072d9cf59 (patch) | |
tree | db9cb9424fbae04decf7a8281a5180f65e5124b9 /fs | |
parent | f4947fbce208990266920d51837e4e7ba9779db1 (diff) | |
download | linux-fsl-qoriq-eaf5f9073533cde21c7121c136f1c3f072d9cf59.tar.xz |
fix shrink_dcache_parent() livelock
Two (or more) concurrent calls of shrink_dcache_parent() on the same dentry may
cause shrink_dcache_parent() to loop forever.
Here's what appears to happen:
1 - CPU0: select_parent(P) finds C and puts it on dispose list, returns 1
2 - CPU1: select_parent(P) locks P->d_lock
3 - CPU0: shrink_dentry_list() locks C->d_lock
dentry_kill(C) tries to lock P->d_lock but fails, unlocks C->d_lock
4 - CPU1: select_parent(P) locks C->d_lock,
moves C from dispose list being processed on CPU0 to the new
dispose list, returns 1
5 - CPU0: shrink_dentry_list() finds dispose list empty, returns
6 - Goto 2 with CPU0 and CPU1 switched
Basically select_parent() steals the dentry from shrink_dentry_list() and thinks
it found a new one, causing shrink_dentry_list() to think it's making progress
and loop over and over.
One way to trigger this is to make udev calls stat() on the sysfs file while it
is going away.
Having a file in /lib/udev/rules.d/ with only this one rule seems to the trick:
ATTR{vendor}=="0x8086", ATTR{device}=="0x10ca", ENV{PCI_SLOT_NAME}="%k", ENV{MATCHADDR}="$attr{address}", RUN+="/bin/true"
Then execute the following loop:
while true; do
echo -bond0 > /sys/class/net/bonding_masters
echo +bond0 > /sys/class/net/bonding_masters
echo -bond1 > /sys/class/net/bonding_masters
echo +bond1 > /sys/class/net/bonding_masters
done
One fix would be to check all callers and prevent concurrent calls to
shrink_dcache_parent(). But I think a better solution is to stop the
stealing behavior.
This patch adds a new dentry flag that is set when the dentry is added to the
dispose list. The flag is cleared in dentry_lru_del() in case the dentry gets a
new reference just before being pruned.
If the dentry has this flag, select_parent() will skip it and let
shrink_dentry_list() retry pruning it. With select_parent() skipping those
dentries there will not be the appearance of progress (new dentries found) when
there is none, hence shrink_dcache_parent() will not loop forever.
Set the flag is also set in prune_dcache_sb() for consistency as suggested by
Linus.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/dcache.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 3c6d311..616fedf 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -243,6 +243,7 @@ static void dentry_lru_add(struct dentry *dentry) static void __dentry_lru_del(struct dentry *dentry) { list_del_init(&dentry->d_lru); + dentry->d_flags &= ~DCACHE_SHRINK_LIST; dentry->d_sb->s_nr_dentry_unused--; dentry_stat.nr_unused--; } @@ -806,6 +807,7 @@ relock: spin_unlock(&dentry->d_lock); } else { list_move_tail(&dentry->d_lru, &tmp); + dentry->d_flags |= DCACHE_SHRINK_LIST; spin_unlock(&dentry->d_lock); if (!--count) break; @@ -1097,14 +1099,19 @@ resume: /* * move only zero ref count dentries to the dispose list. + * + * Those which are presently on the shrink list, being processed + * by shrink_dentry_list(), shouldn't be moved. Otherwise the + * loop in shrink_dcache_parent() might not make any progress + * and loop forever. */ - if (!dentry->d_count) { + if (dentry->d_count) { + dentry_lru_del(dentry); + } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) { dentry_lru_move_list(dentry, dispose); + dentry->d_flags |= DCACHE_SHRINK_LIST; found++; - } else { - dentry_lru_del(dentry); } - /* * We can return to the caller if we have found some (this * ensures forward progress). We'll be coming back to find |