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Date: Mon, 31 May 2004 15:15:05 -0700
From: Andrew Morton <akpm@osdl.org>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: axboe@suse.de, linux-kernel@vger.kernel.org
Subject: Re: loop/highmem related 2.4.26 lockup
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Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> Proc;  loop2
>  >>EIP; e5d145c0 <END_OF_CODE+2597a348/????>   <=====
>  Trace; c0189ec8 <journal_alloc_journal_head+18/80>
>  Trace; c0189fa2 <journal_add_journal_head+52/140>
>  Trace; c0107b92 <__down+82/d0>
>  Trace; c0107d2c <__down_failed+8/c>
>  Trace; c01845fe <.text.lock.transaction+4/246>
>  Trace; c018204a <new_handle+4a/70>
>  Trace; c0182114 <journal_start+a4/c0>
>  Trace; c017bc3c <ext3_writepage_trans_blocks+1c/a0>
>  Trace; c01795ec <ext3_prepare_write+24c/260>
>  Trace; c013349e <find_or_create_page+5e/150>
>  Trace; c01d6f84 <lo_send+124/2e0>
>  Trace; c01d7408 <do_bh_filebacked+b8/c0>
>  Trace; c01d7b84 <loop_thread+224/250>
>  Trace; c0109172 <ret_from_fork+6/20>
>  Trace; c01d7960 <loop_thread+0/250>
>  Trace; c010740e <arch_kernel_thread+2e/40>
>  Trace; c01d7960 <loop_thread+0/250>

You've run out of memory and the loop thread is looping in
journal_alloc_journal_head(), waiting for memory to come free.

Meanwhile, kswapd and bdflush are blocked waiting for I/O which requires
loop thread services to complete.  Deadlock.

A proper fix for this might be fairly complex.  A kludgey fix like the
below might work though.

diff -puN fs/jbd/journal.c~a fs/jbd/journal.c
--- 24/fs/jbd/journal.c~a	2004-05-31 15:12:47.479649360 -0700
+++ 24-akpm/fs/jbd/journal.c	2004-05-31 15:13:15.908327544 -0700
@@ -1728,6 +1728,9 @@ static struct journal_head *journal_allo
 		while (ret == 0) {
 			yield();
 			ret = kmem_cache_alloc(journal_head_cache, GFP_NOFS);
+			if (!ret)
+				ret = kmem_cache_alloc(journal_head_cache,
+							GFP_ATOMIC);
 		}
 	}
 	return ret;
_