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fs/dcache.c: avoid soft-lockup in dput()

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commit 47be61845c775643f1aa4d2a54343549f943c94c upstream.

We triggered soft-lockup under stress test which
open/access/write/close one file concurrently on more than
five different CPUs:

WARN: soft lockup - CPU#0 stuck for 11s! [who:30631]
...
[<ffffffc0003986f8>] dput+0x100/0x298
[<ffffffc00038c2dc>] terminate_walk+0x4c/0x60
[<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8
[<ffffffc00038f780>] filename_lookup+0x38/0xf0
[<ffffffc000391180>] user_path_at_empty+0x78/0xd0
[<ffffffc0003911f4>] user_path_at+0x1c/0x28
[<ffffffc00037d4fc>] SyS_faccessat+0xb4/0x230

->d_lock trylock may failed many times because of concurrently
operations, and dput() may execute a long time.

Fix this by replacing cpu_relax() with cond_resched().
dput() used to be sleepable, so make it sleepable again
should be safe.

Signed-off-by: Wei Fang <fangwei1@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Wei Fang 2016-07-06 11:32:20 +08:00 committed by Greg Kroah-Hartman
parent b6e0a217f6
commit 92f71339bc
1 changed files with 5 additions and 2 deletions
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7
fs/dcache.c
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@ -578,7 +578,6 @@ static struct dentry *dentry_kill(struct dentry *dentry)
failed:
spin_unlock(&dentry->d_lock);
cpu_relax();
return dentry; /* try again with same dentry */
}
@ -752,6 +751,8 @@ void dput(struct dentry *dentry)
return;
repeat:
might_sleep();
rcu_read_lock();
if (likely(fast_dput(dentry))) {
rcu_read_unlock();
@ -783,8 +784,10 @@ repeat:
kill_it:
dentry = dentry_kill(dentry);
if (dentry)
if (dentry) {
cond_resched();
goto repeat;
}
}
EXPORT_SYMBOL(dput);