From 7d06f7f8963d8a705aeda1a5b60a69bfca75935e Mon Sep 17 00:00:00 2001 From: Wei Fang Date: Wed, 6 Jul 2016 11:32:20 +0800 Subject: fs/dcache.c: avoid soft-lockup in dput() [ Upstream commit 47be61845c775643f1aa4d2a54343549f943c94c ] 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] ... [] dput+0x100/0x298 [] terminate_walk+0x4c/0x60 [] path_lookupat+0x5cc/0x7a8 [] filename_lookup+0x38/0xf0 [] user_path_at_empty+0x78/0xd0 [] user_path_at+0x1c/0x28 [] 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. Cc: Signed-off-by: Wei Fang Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/dcache.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 2c75b393d31a..660857431b1c 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -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); -- cgit v1.2.3