linux-kernel - Re: 2.6.25-$sha1: RIP call_for_each

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Message-ID: <20080429090604.GK12774@kernel.dk>
Date:	Tue, 29 Apr 2008 11:06:05 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25-$sha1: RIP call_for_each_cic+0x25/0x50

On Tue, Apr 29 2008, Alexey Dobriyan wrote:
> On Mon, Apr 28, 2008 at 11:55:09PM +0400, Alexey Dobriyan wrote:
> > On Mon, Apr 28, 2008 at 02:04:13PM +0200, Jens Axboe wrote:
> > > On Mon, Apr 28 2008, Andrew Morton wrote:
> > > > On Mon, 28 Apr 2008 02:55:53 +0400 Alexey Dobriyan <adobriyan@...il.com> wrote:
> > > > 
> > > > > This happened while ~90 cross-compile jobs were running in parallel on
> > > > > ext2/noatime partition (slowly -- much debugging was on)
> > > > > 
> > > > > 
> > > > > general protection fault: 0000 [1] PREEMPT SMP DEBUG_PAGEALLOC
> > > > > CPU 0 
> > > > > Modules linked in: ext2 nf_conntrack_irc ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 xt_state nf_conntrack iptable_filter ip_tables x_tables usblp uhci_hcd ehci_hcd usbcore sr_mod cdrom
> > > > > Pid: 16483, comm: as Not tainted 2.6.25-c3bf9bc243092c53946fd6d8ebd6dc2f4e572d48 #1
> > > > > RIP: 0010:[<ffffffff80307525>]  [<ffffffff80307525>] call_for_each_cic+0x25/0x50
> > > > > RSP: 0018:ffff810170811e58  EFLAGS: 00010202
> > > > > RAX: 6b6b6b6b6b6b6b6b RBX: 6b6b6b6b6b6b6b6b RCX: 0000000000000000
> > > > > RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff81010ff92000
> > > > > RBP: ffff810170811e78 R08: 0000000000000001 R09: 0000000000000000
> > > > > R10: 0000000000000000 R11: ffff8100010069d8 R12: ffff810138ada300
> > > > > R13: ffffffff803075b0 R14: ffff81017fcd2000 R15: ffff81010ff92168
> > > > > FS:  00002ac3462426f0(0000) GS:ffffffff805d0000(0000) knlGS:0000000000000000
> > > > > CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > > > > CR2: 00002ab602550000 CR3: 000000013609d000 CR4: 0000000000000660
> > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > > > > Process as (pid: 16483, threadinfo ffff810170810000, task ffff81010ff92000)
> > > > > Stack:  ffff810170811e88 ffff810138ada300 0000000000000010 ffff81010ff92100
> > > > >  ffff810170811e88 ffffffff80307580 ffff810170811ea8 ffffffff80302a55
> > > > >  ffff81010ff92100 ffff810138ada300 ffff810170811ec8 ffffffff80302b1f
> > > > > Call Trace:
> > > > >  [<ffffffff80307580>] cfq_free_io_context+0x10/0x20
> > > > >  [<ffffffff80302a55>] put_io_context+0x85/0x90
> > > > >  [<ffffffff80302b1f>] exit_io_context+0x8f/0xb0
> > > > >  [<ffffffff80235d19>] do_exit+0x549/0x780
> > > > >  [<ffffffff80235f8e>] do_group_exit+0x3e/0xb0
> > > > >  [<ffffffff80236012>] sys_exit_group+0x12/0x20
> > > > >  [<ffffffff8020b6db>] system_call_after_swapgs+0x7b/0x80
> > > > > 
> > > > > 
> > > > > Code: 84 00 00 00 00 00 55 48 89 e5 41 55 49 89 f5 41 54 49 89 fc 53 48 83 ec 08 e8 18 e1 f5 ff 49 8b 44 24 68 48 85 c0 74 1e 48 89 c3 <48> 8b 03 48 8d 73 88 4c 89 e7 0f 18 08 41 ff d5 48 8b 03 48 85 
> > > > > RIP  [<ffffffff80307525>] call_for_each_cic+0x25/0x50
> > > > >  RSP <ffff810170811e58>
> > > > > ---[ end trace ca143223eefdc828 ]---
> > > > > Fixing recursive fault but reboot is needed!
> > > > cfq-iosched.c hasn't been altered (yet) so it might not be a regression.
> 
> 
> > > It's not a regression, it's definitely in 2.6.25 as well. So that's a
> > > bit scary, I've been looking over this stuff this morning but haven't
> > > pin pointed anything yet.
> > > 
> > > Alexey, is this something that reproduces for you?
> > 
> > Not yet, second run of same workload went fine and I've never seen such
> > oopses before.
> 
> And it oopses the very same way on the third run. as(1) again.
> So if there are any debugging patches, let me know.

There seems to be a small race in the destructor path, can you see if
this makes a difference?

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index e34df7c..012f065 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -41,8 +41,8 @@ int put_io_context(struct io_context *ioc)
 		rcu_read_lock();
 		if (ioc->aic && ioc->aic->dtor)
 			ioc->aic->dtor(ioc->aic);
-		rcu_read_unlock();
 		cfq_dtor(ioc);
+		rcu_read_unlock();
 
 		kmem_cache_free(iocontext_cachep, ioc);
 		return 1;

-- 
Jens Axboe

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