From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joel Becker <Joel.Becker@oracle.com>
Date: Sat, 7 Aug 2010 11:39:52 -0700
Subject: [Ocfs2-devel] [PATCH V4] Fix the nested PR lock calling issue
	in ACL
In-Reply-To: <20100728052106.GA9373@linux-jjzhang>
References: <20100728052106.GA9373@linux-jjzhang>
Message-ID: <20100807183952.GD3699@mail.oracle.com>
List-Id: <ocfs2-devel.oss.oracle.com>
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To: ocfs2-devel@oss.oracle.com

On Wed, Jul 28, 2010 at 01:21:06PM +0800, Jiaju Zhang wrote:
> Hi,
> 
> Thanks a lot for all the review and comments so far;) I'd like to send
> the improved (V4) version of this patch.
> 
> This patch fixes a deadlock in OCFS2 ACL. We found this bug in OCFS2
> and Samba integration using scenario, the symptom is several smbd
> processes will be hung under heavy workload. Finally we found out it
> is the nested PR lock calling that leads to this deadlock:
> 
>  node1        node2
>               gr PR
>                 |
>                 V
>  PR(EX)---> BAST:OCFS2_LOCK_BLOCKED
>                 |
>                 V
>               rq PR
>                 |
>                 V
>               wait=1
> 
> After requesting the 2nd PR lock, the process "smbd" went into D
> state. It can only be woken up when the 1st PR lock's RO holder equals
> zero. There should be an ocfs2_inode_unlock in the calling path later
> on, which can decrement the RO holder. But since it has been in
> uninterruptible sleep, the unlock function has no chance to be called.
> 
> The related stack trace is:
> smbd          D ffff8800013d0600     0  9522   5608 0x00000000
>  ffff88002ca7fb18 0000000000000282 ffff88002f964500 ffff88002ca7fa98
>  ffff8800013d0600 ffff88002ca7fae0 ffff88002f964340 ffff88002f964340
>  ffff88002ca7ffd8 ffff88002ca7ffd8 ffff88002f964340 ffff88002f964340
> Call Trace:
> [<ffffffff80350425>] schedule_timeout+0x175/0x210
> [<ffffffff8034f580>] wait_for_common+0xf0/0x210
> [<ffffffffa03e12b9>] __ocfs2_cluster_lock+0x3b9/0xa90 [ocfs2]
> [<ffffffffa03e7665>] ocfs2_inode_lock_full_nested+0x255/0xdb0 [ocfs2]
> [<ffffffffa0446019>] ocfs2_get_acl+0x69/0x120 [ocfs2]
> [<ffffffffa0446368>] ocfs2_check_acl+0x28/0x80 [ocfs2]
> [<ffffffff800e3507>] acl_permission_check+0x57/0xb0
> [<ffffffff800e357d>] generic_permission+0x1d/0xc0
> [<ffffffffa03eecea>] ocfs2_permission+0x10a/0x1d0 [ocfs2]
> [<ffffffff800e3f65>] inode_permission+0x45/0x100
> [<ffffffff800d86b3>] sys_chdir+0x53/0x90
> [<ffffffff80007458>] system_call_fastpath+0x16/0x1b
> [<00007f34a4ef6927>] 0x7f34a4ef6927
> 
> For details, please see:
> https://bugzilla.novell.com/show_bug.cgi?id=614332 and
> http://oss.oracle.com/bugzilla/show_bug.cgi?id=1278
> 
> Signed-off-by: Jiaju Zhang <jjzhang@suse.de>
> Acked-by: Mark Fasheh <mfasheh@suse.com>

This patch is now in the fixes branch of ocfs2.git.

Joel
-- 

Life's Little Instruction Book #43

	"Never give up on somebody.  Miracles happen every day."

Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127