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Re: Still seeing hangs in xlog_grant_log_space

To: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
Subject: Re: Still seeing hangs in xlog_grant_log_space
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 12 Jun 2012 09:53:37 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <33996217.post@xxxxxxxxxxxxxxx>
References: <CADLDEKsP4DsXf_G07ub+a-ODbrJbsiprRJUX1fJdaQ41TB7+Xg@xxxxxxxxxxxxxx> <CAH4wwdGWHSZoveLJMxu5pjr22NEEeW7oG8TS+snoM8RY=ZeRmg@xxxxxxxxxxxxxx> <CADLDEKsGtsw-rrSOE7gY4T81u+p41b34ixv0B7Dh07afJ73n2w@xxxxxxxxxxxxxx> <CAH4wwdFu7DEkHFZ5Bf7_PtLPsG0hUyUDoov03q=82R6t+QkERg@xxxxxxxxxxxxxx> <20120605235447.GF22848@dastard> <4FCF5DB9.2000808@xxxxxxxxxx> <4FCF9655.3070300@xxxxxxx> <33996217.post@xxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Jun 11, 2012 at 01:42:31PM -0700, Chris J Arges wrote:
> Mark Tinguely-3 wrote:
> > 
> > The perl script to recreate this problem is very similar to xfstest 273.
> > I use that because it avoids all the filesystem mount/unmount that
> > happen between the test 273 loops. You can build the log size that you
> > want to test, create the directories and let it run until it hangs.
> > 
> I tested xfstest 273, and it looks like it exhibits a different issue than
> the OP in this thread.
> For example, if I run this test in a while [1] loop, I get the following
> backtrace:
> [16413.073946] XFS (sda5): Invalid block length (0xfffff48b) for buffer

That looks bad. How big is the log on this filesystem?

> [16413.073963] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000130
> [16413.074274] IP: [<ffffffffa02bb870>] uuid_is_nil+0x10/0x50 [xfs]

I can't really see how this function can get a null pointer
dereference. It checks the pointer passed in for being null before
doing anything, and otherwise it just increments and dereferences
the char pointer 16 times. I can't see how that results in a NULL
being dereferenced - I might just be blind though.


Dave Chinner

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