Re: Deadlock possibly caused by too_many_isolated.

[KOSAKI Motohiro]

> On Tue, Oct 19, 2010 at 06:06:21PM +0800, Torsten Kaiser wrote:
> > On Tue, Oct 19, 2010 at 10:43 AM, Torsten Kaiser
> > <just.for.lkml@xxxxxxxxxxxxxx> wrote:
> > > On Tue, Oct 19, 2010 at 1:11 AM, Neil Brown <neilb@xxxxxxx> wrote:
> > >> Yes, thanks for the report.
> > >> This is a real bug exactly as you describe.
> > >>
> > >> This is how I think I will fix it, though it needs a bit of review and
> > >> testing before I can be certain.
> > >> Also I need to check raid10 etc to see if they can suffer too.
> > >>
> > >> If you can test it I would really appreciate it.
> > >
> > > I did test it, but while it seemed to fix the deadlock, the system
> > > still got unusable.
> > > The still running "vmstat 1" showed that the swapout was still
> > > progressing, but at a rate of ~20k sized bursts every 5 to 20 seconds.
> > >
> > > I also tried to additionally add Wu's patch:
> > > --- linux-next.orig/mm/vmscan.c 2010-10-13 12:35:14.000000000 +0800
> > > +++ linux-next/mm/vmscan.c   Â2010-10-19 00:13:04.000000000 +0800
> > > @@ -1163,6 +1163,13 @@ static int too_many_isolated(struct zone
> > > Â Â Â Â Â Â Â isolated = zone_page_state(zone, NR_ISOLATED_ANON);
> > > Â Â Â }
> > >
> > > + Â Â Â /*
> > > + Â Â Â Â* GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so that
> > > + Â Â Â Â* they won't get blocked by normal ones and form circular deadlock.
> > > + Â Â Â Â*/
> > > + Â Â Â if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
> > > + Â Â Â Â Â Â Â inactive >>= 3;
> > > +
> > > Â Â Â return isolated > inactive;
> > >
> > > Either it did help somewhat, or I was more lucky on my second try, but
> > > this time I needed ~5 tries instead of only 2 to get the system mostly
> > > stuck again. On the testrun with Wu's patch the writeout pattern was
> > > more stable, a burst of ~80kb each 20 seconds. But I would suspect
> > > that the size of the burst is rather random.
> > >
> > > I do have a complete SysRq+T dump from the first run, I can send that
> > > to anyone how wants it.
> > > (It's 190k so I don't want not spam it to the list)
> > 
> > Is this call trace from the SysRq+T violation the rule to only
> > allocate one bio from bio_alloc() until its submitted?
> > 
> > [  549.700038] Call Trace:
> > [  549.700038]  [<ffffffff81566b54>] schedule_timeout+0x144/0x200
> > [  549.700038]  [<ffffffff81045cd0>] ? process_timeout+0x0/0x10
> > [  549.700038]  [<ffffffff81565e22>] io_schedule_timeout+0x42/0x60
> > [  549.700038]  [<ffffffff81083123>] mempool_alloc+0x163/0x1b0
> > [  549.700038]  [<ffffffff81053560>] ? autoremove_wake_function+0x0/0x40
> > [  549.700038]  [<ffffffff810ea2b9>] bio_alloc_bioset+0x39/0xf0
> > [  549.700038]  [<ffffffff810ea38d>] bio_clone+0x1d/0x50
> > [  549.700038]  [<ffffffff814318ed>] make_request+0x23d/0x850
> > [  549.700038]  [<ffffffff81082e20>] ? mempool_alloc_slab+0x10/0x20
> > [  549.700038]  [<ffffffff81045cd0>] ? process_timeout+0x0/0x10
> > [  549.700038]  [<ffffffff81436e63>] md_make_request+0xc3/0x220
> > [  549.700038]  [<ffffffff81083099>] ? mempool_alloc+0xd9/0x1b0
> > [  549.700038]  [<ffffffff811ec153>] generic_make_request+0x1b3/0x370
> > [  549.700038]  [<ffffffff810ea2d6>] ? bio_alloc_bioset+0x56/0xf0
> > [  549.700038]  [<ffffffff811ec36a>] submit_bio+0x5a/0xd0
> > [  549.700038]  [<ffffffff81080cf5>] ? unlock_page+0x25/0x30
> > [  549.700038]  [<ffffffff810a871e>] swap_writepage+0x7e/0xc0
> > [  549.700038]  [<ffffffff81090d99>] shmem_writepage+0x1c9/0x240
> > [  549.700038]  [<ffffffff8108c9cb>] pageout+0x11b/0x270
> > [  549.700038]  [<ffffffff8108cd78>] shrink_page_list+0x258/0x4d0
> > [  549.700038]  [<ffffffff8108d9e7>] shrink_inactive_list+0x187/0x310
> > [  549.700038]  [<ffffffff8102dcb1>] ? __wake_up_common+0x51/0x80
> > [  549.700038]  [<ffffffff811fc8b2>] ? cpumask_next_and+0x22/0x40
> > [  549.700038]  [<ffffffff8108e1c0>] shrink_zone+0x3e0/0x470
> > [  549.700038]  [<ffffffff8108e797>] try_to_free_pages+0x157/0x410
> > [  549.700038]  [<ffffffff81087c92>] __alloc_pages_nodemask+0x412/0x760
> > [  549.700038]  [<ffffffff810b27d6>] alloc_pages_current+0x76/0xe0
> > [  549.700038]  [<ffffffff810b6dad>] new_slab+0x1fd/0x2a0
> > [  549.700038]  [<ffffffff81045cd0>] ? process_timeout+0x0/0x10
> > [  549.700038]  [<ffffffff810b8721>] __slab_alloc+0x111/0x540
> > [  549.700038]  [<ffffffff81059961>] ? prepare_creds+0x21/0xb0
> > [  549.700038]  [<ffffffff810b92bb>] kmem_cache_alloc+0x9b/0xa0
> > [  549.700038]  [<ffffffff81059961>] prepare_creds+0x21/0xb0
> > [  549.700038]  [<ffffffff8104a919>] sys_setresgid+0x29/0x120
> > [  549.700038]  [<ffffffff8100242b>] system_call_fastpath+0x16/0x1b
> > [  549.700038]  ffff88011e125ea8 0000000000000046 ffff88011e125e08
> > ffffffff81073c59
> > [  549.700038]  0000000000012780 ffff88011ea905b0 ffff88011ea90808
> > ffff88011e125fd8
> > [  549.700038]  ffff88011ea90810 ffff88011e124010 0000000000012780
> > ffff88011e125fd8
> > 
> > swap_writepage() uses get_swap_bio() which uses bio_alloc() to get one
> > bio. That bio is the submitted, but the submit path seems to get into
> > make_request from raid1.c and that allocates a second bio from
> > bio_alloc() via bio_clone().
> > 
> > I am seeing this pattern (swap_writepage calling
> > md_make_request/make_request and then getting stuck in mempool_alloc)
> > more than 5 times in the SysRq+T output...
> 
> I bet the root cause is the failure of pool->alloc(__GFP_NORETRY)
> inside mempool_alloc(), which can be fixed by this patch.
> 
> Thanks,
> Fengguang
> ---
> 
> concurrent direct page reclaim problem
> 
>   __GFP_NORETRY page allocations may fail when there are many concurrent page
>   allocating tasks, but not necessary in real short of memory. The root cause
>   is, tasks will first run direct page reclaim to free some pages from the LRU
>   lists and put them to the per-cpu page lists and the buddy system, and then
>   try to get a free page from there.  However the free pages reclaimed by this
>   task may be consumed by other tasks when the direct reclaim task is able to
>   get the free page for itself.
> 
>   Let's retry it a bit harder.
> 
> --- linux-next.orig/mm/page_alloc.c	2010-10-20 13:44:50.000000000 +0800
> +++ linux-next/mm/page_alloc.c	2010-10-20 13:50:54.000000000 +0800
> @@ -1700,7 +1700,7 @@ should_alloc_retry(gfp_t gfp_mask, unsig
>  				unsigned long pages_reclaimed)
>  {
>  	/* Do not loop if specifically requested */
> -	if (gfp_mask & __GFP_NORETRY)
> +	if (gfp_mask & __GFP_NORETRY && pages_reclaimed > (1 << (order + 12)))
>  		return 0;
>  
>  	/*

SLUB usually try high order allocation with __GFP_NORETRY at first. In
other words, It strongly depend on __GFP_NORETRY don't any retry. I'm
worry this...

And, in this case, stucked tasks have PF_MEMALLOC. allocation with PF_MEMALLOC
failure mean this zone have zero memory purely. So, retrying don't solve anything.

And I think the root cause is in another.

bio_clone() use fs_bio_set internally.

	struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
	{
	        struct bio *b = bio_alloc_bioset(gfp_mask, bio->bi_max_vecs, fs_bio_set);
	...

and fs_bio_set is initialized very small pool size.

	#define BIO_POOL_SIZE 2
	static int __init init_bio(void)
	{
		..
	        fs_bio_set = bioset_create(BIO_POOL_SIZE, 0);

So, I think raid1.c need to use their own bioset instead fs_bio_set.
otherwise, bio pool exshost can happen very easily.

But I'm not sure. I'm not IO expert.




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