From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp1040.oracle.com ([156.151.31.81]:36702 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753955AbcIPHu7 (ORCPT ); Fri, 16 Sep 2016 03:50:59 -0400 Subject: Re: [PATCH v2] fs/dcache.c: avoid soft-lockup in dput() To: Wei Fang , viro@zeniv.linux.org.uk References: <1466564475-30417-1-git-send-email-fangwei1@huawei.com> Cc: linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org, jack@suse.com, axboe@kernel.dk, tj@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org From: Vaishali Thakkar Message-ID: <57DBA3FF.4080201@oracle.com> Date: Fri, 16 Sep 2016 13:19:19 +0530 MIME-Version: 1.0 In-Reply-To: <1466564475-30417-1-git-send-email-fangwei1@huawei.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On Wednesday 22 June 2016 08:31 AM, Wei Fang wrote: > 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. Hi, Just a question regarding this change. As after this change dput() is sleepable, is it still safe to use if under the spinlock in the function d_prune_aliases? Thanks > Cc: > Signed-off-by: Wei Fang > --- > Changes v1->v2: > - add might_sleep() to annotate that dput() can sleep > > fs/dcache.c | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index d5ecc6e..074fc1c 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -578,7 +578,7 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > failed: > spin_unlock(&dentry->d_lock); > - cpu_relax(); > + cond_resched(); > return dentry; /* try again with same dentry */ > } > > @@ -752,6 +752,8 @@ void dput(struct dentry *dentry) > return; > > repeat: > + might_sleep(); > + > rcu_read_lock(); > if (likely(fast_dput(dentry))) { > rcu_read_unlock(); > -- Vaishali