Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.6 46/56] fs/dcache.c: avoid soft-lockup in dput() | Date | Sun, 14 Aug 2016 22:37:50 +0200 |
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4.6-stable review patch. If anyone has any objections, please let me know.
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From: Wei Fang <fangwei1@huawei.com>
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>
--- fs/dcache.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/fs/dcache.c +++ b/fs/dcache.c @@ -578,7 +578,6 @@ static struct dentry *dentry_kill(struct 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);
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