linux-kernel - Re: system hang on latest git

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Date:	Tue, 29 Jan 2008 21:16:48 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-ia64@...r.kernel.org
Subject: Re: system hang on latest git

On Tue, Jan 29 2008, Jens Axboe wrote:
> On Tue, Jan 29 2008, Luck, Tony wrote:
> > I pulled Linus' tree this morning (git head = 0ba6c33bcddc64a54b5f1c25a696c4767dc76292)
> > and built for ia64 (using arch/ia64/configs/tiger_defconfig).   System booted
> > OK, but when I stressed it a little (building another kernel with "make -j32")
> > it hung.
> > 
> > The console has a bunch (98) of warnings about tasks blocked for more than 120
> > seconds like this:
> > INFO: task grep:9168 blocked for more than 120 seconds.
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > 
> > Call Trace:
> >  [<a000000100704120>] schedule+0x11c0/0x1340
> >                                 sp=e0000001ed8afbf0 bsp=e0000001ed8a1280
> >  [<a00000010024e720>] do_get_write_access+0x660/0xbe0
> >                                 sp=e0000001ed8afc20 bsp=e0000001ed8a1208
> >  [<a00000010024f060>] journal_get_write_access+0x40/0x80
> >                                 sp=e0000001ed8afca0 bsp=e0000001ed8a11c8
> >  [<a000000100245db0>] __ext3_journal_get_write_access+0x30/0xa0
> >                                 sp=e0000001ed8afca0 bsp=e0000001ed8a1190
> >  [<a00000010022dea0>] ext3_reserve_inode_write+0x80/0x120
> >                                 sp=e0000001ed8afca0 bsp=e0000001ed8a1158
> >  [<a00000010022df70>] ext3_mark_inode_dirty+0x30/0x80
> >                                 sp=e0000001ed8afca0 bsp=e0000001ed8a1130
> >  [<a000000100232530>] ext3_dirty_inode+0xd0/0x120
> >                                 sp=e0000001ed8afcc0 bsp=e0000001ed8a1100
> >  [<a000000100170e20>] __mark_inode_dirty+0xa0/0x3e0
> >                                 sp=e0000001ed8afcc0 bsp=e0000001ed8a10b0
> >  [<a00000010015b570>] touch_atime+0x310/0x340
> >                                 sp=e0000001ed8afcc0 bsp=e0000001ed8a1088
> >  [<a0000001000d6c20>] do_generic_mapping_read+0x780/0x7a0
> >                                 sp=e0000001ed8afce0 bsp=e0000001ed8a0fe0
> >  [<a0000001000db250>] generic_file_aio_read+0x290/0x340
> >                                 sp=e0000001ed8afce0 bsp=e0000001ed8a0f80
> >  [<a00000010012c990>] do_sync_read+0x170/0x200
> >                                 sp=e0000001ed8afd10 bsp=e0000001ed8a0f40
> >  [<a00000010012cbd0>] vfs_read+0x1b0/0x2e0
> >                                 sp=e0000001ed8afe20 bsp=e0000001ed8a0ef0
> >  [<a00000010012d250>] sys_read+0x70/0xe0
> >                                 sp=e0000001ed8afe20 bsp=e0000001ed8a0e78
> >  [<a00000010000a4a0>] ia64_ret_from_syscall+0x0/0x20
> >                                 sp=e0000001ed8afe30 bsp=e0000001ed8a0e78
> > 
> > 
> > [The stack trace has several variations ... some from sys_read(), some from
> > sys_open(), some from sys_execve(), some from sys_mmap() etc. 84/98 stack
> > traces pass through the touch_atime->__mark_inode_dirty path ... all 98
> > are attached]
> > 
> > A quick dig into processor state shows 8 cpus are idle.  7 are spinning
> > in __spin_lock_irq() from __make_request() and one is in spin_lock() from
> > as_merged_requests().
> 
> Looks like a deadlock on queue lock and ioc lock, but I don't see
> immediately what the problem is. I can't stick around for longer
> tonight, but I'll get to the bottom of this tomorrow.

Actually, can you try this? It has a known race but nothing to worry
about, and it removes ioc->lock from irq context.

diff --git a/block/as-iosched.c b/block/as-iosched.c
index b201d16..585aad2 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -235,10 +235,8 @@ static void as_put_io_context(struct request *rq)
 	aic = RQ_IOC(rq)->aic;
 
 	if (rq_is_sync(rq) && aic) {
-		spin_lock(&aic->lock);
 		set_bit(AS_TASK_IORUNNING, &aic->state);
 		aic->last_end_request = jiffies;
-		spin_unlock(&aic->lock);
 	}
 
 	put_io_context(RQ_IOC(rq));

-- 
Jens Axboe

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