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Date: Fri, 14 Dec 2001 09:26:42 -0800
From: Andrew Morton <akpm@zip.com.au>
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To: Chris Mason <mason@suse.com>
CC: Johan Ekenberg <johan@ekenberg.se>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        jack@suse.cz, linux-kernel@vger.kernel.org
Subject: Re: Lockups with 2.4.14 and 2.4.16
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Chris Mason wrote:
> 
> Ok, Johan sent along stack traces, and the deadlock works a little like this:
> 
> linux-2.4.16 + reiserfs + quota v2
> 
> kswapd ->
> prune_icache->dispose_list->dquot_drop->commit_dquot->generic_file_write->
> mark_inode_dirty->journal_begin-> wait for trans to end

uh-huh.

> Some process in the transaction is waiting on kswapd to free ram.

This is unfamiliar.  Where does a process block on kswapd in this
manner?  Not __alloc_pages I think.
 
> So, this will hit any journaled FS that uses quotas and logs inodes under
> during a write.  ext3 doesn't seem to do special things for quota anymore, so
> it should be affected too.

mm.. most of the ext3 damage-avoidance hacks are around writepage().

> The only fix I see is to make sure kswapd doesn't run shrink_icache, and to
> have it done via a dedicated daemon instead.  Does anyone have a better idea?

Well, we already need to do something like that to prevent the
abuse of keventd in there.  It appears that somebody had a
problem with deadlocks doing the inode writeout in kswapd but
missed the quota problem.

Is it possible for the quota code to just bale out if PF_MEMALLOC
is set?  To leave the dquot dirty?

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