From: Trond Myklebust <trond.myklebust@primarydata.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
lawa@nvidia.com,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>
Subject: Re: RCU caching regression in kernel v4.1+
Date: Thu, 08 Oct 2015 08:54:40 -0400 [thread overview]
Message-ID: <1444308880.43040.1.camel@primarydata.com> (raw)
In-Reply-To: <CAHQdGtQTDeYN4ZQn8=zV4WwTQG-FWoLNb4H-kTwJo_nRsy3g6g@mail.gmail.com>
On Wed, 2015-10-07 at 14:57 -0400, Trond Myklebust wrote:
> Hi Al,
>
> Please could you take a look at the bugzilla entry in
> https://bugzilla.kernel.org/show_bug.cgi?id=104911 ?
>
> It describes a NFS caching regression that appears to be caused by
> commit 766c4cbfacd8634d7580bac6a1b8456e63de3e84 ("namei:
> d_is_negative() should be checked before ->d_seq validation").
>
> Shouldn't that test for 'if (negative) return -ENOENT;' happen after
> the call to d_revalidate() in lookup_fast()? If not, we can end up
> caching negative dentries forever, AFAICS...
>
> Cheers
> Trond
Leandro, can you please test if the following patch helps in any way?
Cheers
Trond
8<-----------------------------------------------------------------
>From eb61ece5739bb2f3b6d03dd8ca8e335bf0d12687 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Thu, 8 Oct 2015 08:44:00 -0400
Subject: [PATCH] namei: results of d_is_negative() should be checked after
dentry revalidation
Leandro Awa writes:
After switching to version 4.1.6, our parallelized and distributed workflows now fail consistently with errors of the form:
T34: ./regex.c:39:22: error: config.h: No such file or directory
>From our 'git bisect' testing, the following commit appears to be
the possible cause of the behavior we've been seeing: commit 766c4cbfacd8
The issue is that revalidation may cause the dentry to be dropped in NFS
if, say, the client notes that the directory timestamps have changed.
Reported-by: Leandro Awa <lawa@nvidia.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=104911
Fixes: 766c4cbfacd8 ("namei: d_is_negative() should be checked...")
Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
fs/namei.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 726d211db484..33e9495a3129 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1558,8 +1558,6 @@ static int lookup_fast(struct nameidata *nd,
negative = d_is_negative(dentry);
if (read_seqcount_retry(&dentry->d_seq, seq))
return -ECHILD;
- if (negative)
- return -ENOENT;
/*
* This sequence count validates that the parent had no
@@ -1580,6 +1578,12 @@ static int lookup_fast(struct nameidata *nd,
goto unlazy;
}
}
+ /*
+ * Note: do negative dentry check after revalidation in
+ * case that drops it.
+ */
+ if (negative)
+ return -ENOENT;
path->mnt = mnt;
path->dentry = dentry;
if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
--
2.4.3
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com
WARNING: multiple messages have this Message-ID (diff)
From: Trond Myklebust <trond.myklebust@primarydata.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
lawa@nvidia.com,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>
Subject: Re: RCU caching regression in kernel v4.1+
Date: Thu, 08 Oct 2015 08:54:40 -0400 [thread overview]
Message-ID: <1444308880.43040.1.camel@primarydata.com> (raw)
In-Reply-To: <CAHQdGtQTDeYN4ZQn8=zV4WwTQG-FWoLNb4H-kTwJo_nRsy3g6g@mail.gmail.com>
On Wed, 2015-10-07 at 14:57 -0400, Trond Myklebust wrote:
> Hi Al,
>
> Please could you take a look at the bugzilla entry in
> https://bugzilla.kernel.org/show_bug.cgi?id=104911 ?
>
> It describes a NFS caching regression that appears to be caused by
> commit 766c4cbfacd8634d7580bac6a1b8456e63de3e84 ("namei:
> d_is_negative() should be checked before ->d_seq validation").
>
> Shouldn't that test for 'if (negative) return -ENOENT;' happen after
> the call to d_revalidate() in lookup_fast()? If not, we can end up
> caching negative dentries forever, AFAICS...
>
> Cheers
> Trond
Leandro, can you please test if the following patch helps in any way?
Cheers
Trond
8<-----------------------------------------------------------------
next prev parent reply other threads:[~2015-10-08 12:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-07 18:57 RCU caching regression in kernel v4.1+ Trond Myklebust
2015-10-07 18:57 ` Trond Myklebust
2015-10-08 12:54 ` Trond Myklebust [this message]
2015-10-08 12:54 ` Trond Myklebust
[not found] ` <1444308880.43040.1.camel-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>
2015-10-08 17:28 ` Leandro Awa
2015-10-08 17:28 ` Leandro Awa
2015-10-09 0:01 ` Leandro Awa
2015-10-09 0:01 ` Leandro Awa
2015-10-09 17:44 ` [PATCH] namei: results of d_is_negative() should be checked after dentry revalidation Trond Myklebust
2015-10-09 17:44 ` Trond Myklebust
2015-10-09 17:44 ` Trond Myklebust
2015-10-10 0:19 ` Linus Torvalds
2015-10-10 1:36 ` Al Viro
2015-10-10 1:36 ` Al Viro
2015-10-10 17:13 ` Al Viro
2015-10-10 17:13 ` Al Viro
2015-10-10 17:19 ` Linus Torvalds
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