From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Wei Fang , Al Viro Subject: [PATCH 4.7 31/41] fs/dcache.c: avoid soft-lockup in dput() Date: Sun, 14 Aug 2016 22:38:57 +0200 Message-Id: <20160814202533.483010792@linuxfoundation.org> In-Reply-To: <20160814202531.818402015@linuxfoundation.org> References: <20160814202531.818402015@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.7-stable review patch. If anyone has any objections, please let me know. ------------------ From: Wei Fang 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] ... [] 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. Signed-off-by: Wei Fang Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -622,7 +622,6 @@ static struct dentry *dentry_kill(struct failed: spin_unlock(&dentry->d_lock); - cpu_relax(); return dentry; /* try again with same dentry */ } @@ -796,6 +795,8 @@ void dput(struct dentry *dentry) return; repeat: + might_sleep(); + rcu_read_lock(); if (likely(fast_dput(dentry))) { rcu_read_unlock(); @@ -829,8 +830,10 @@ repeat: kill_it: dentry = dentry_kill(dentry); - if (dentry) + if (dentry) { + cond_resched(); goto repeat; + } } EXPORT_SYMBOL(dput);