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From: Vivek Goyal <vgoyal@redhat.com>
To: Kent Overstreet <koverstreet@google.com>
Cc: Tejun Heo <tj@kernel.org>,
	linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
	dm-devel@redhat.com, mpatocka@redhat.com, bharrosh@panasas.com,
	Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers
Date: Wed, 29 Aug 2012 08:57:59 -0400	[thread overview]
Message-ID: <20120829125759.GB12504@redhat.com> (raw)
In-Reply-To: <20120829032558.GA22214@moria.home.lan>

On Tue, Aug 28, 2012 at 08:25:58PM -0700, Kent Overstreet wrote:

[..]
> Except that when thread a goes to punt those blocked bios to its
> rescuer, it punts _all_ the bios on current->bio_list. Even those
> generated by/belonging to other bio_sets.
> 
> So thread 1 in device b punts bios to its rescuer, thread 2
> 
> But thread 2 ends up with bios for both device a and b - because they're
> stacked.

Ok, just to add more details to above example. Say we have device A stacked
on top of B and B stacked on top of C. Say a bio a is submitted to device A
and is splitted in two bios b1 and b2. Now b1 is sumbitted to device B and is
splitted in c1 and c2. Now current bio list has three bios. b2, c1 and c2.
If submitter is now about to block on any bio set, then all tree bios
b2, c1, c2 will punted to rescue thread and submssion of b2 will again block
resulting in blocking rescue thread itself.

I would say keep all the bio splitting patches and any fixes w.r.t
deadlocks in a seprate series. As this is little complicated and a lot
of is just theoritical corner cases. If you limit this series to just
bio_set related cleanups, it becomes more acceptable for inclusion.

Thanks
Vivek

  reply	other threads:[~2012-08-29 12:58 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-28 17:37 [PATCH v7 0/9] Block cleanups, deadlock fix Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 1/9] block: Generalized bio pool freeing Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 2/9] dm: Use bioset's front_pad for dm_rq_clone_bio_info Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 3/9] block: Add bio_reset() Kent Overstreet
2012-08-28 20:31   ` Tejun Heo
2012-08-28 22:17     ` Kent Overstreet
2012-08-28 22:53       ` Kent Overstreet
2012-09-01  2:23       ` Tejun Heo
2012-09-05 20:13         ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 4/9] pktcdvd: Switch to bio_kmalloc() Kent Overstreet
2012-08-28 20:32   ` Tejun Heo
2012-08-28 22:24     ` Kent Overstreet
2012-09-04  9:05     ` Jiri Kosina
2012-09-05 19:44       ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 5/9] block: Kill bi_destructor Kent Overstreet
2012-08-28 20:36   ` Tejun Heo
2012-08-28 22:07     ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 6/9] block: Consolidate bio_alloc_bioset(), bio_kmalloc() Kent Overstreet
2012-08-28 20:41   ` Tejun Heo
2012-08-28 22:03     ` Kent Overstreet
2012-09-01  2:17       ` Tejun Heo
2012-08-28 17:37 ` [PATCH v7 7/9] block: Add bio_clone_bioset(), bio_clone_kmalloc() Kent Overstreet
2012-08-28 20:44   ` Tejun Heo
2012-08-28 22:05     ` Kent Overstreet
2012-09-01  2:19       ` Tejun Heo
2012-08-28 17:37 ` [PATCH v7 8/9] block: Reorder struct bio_set Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Kent Overstreet
2012-08-28 20:49   ` Tejun Heo
2012-08-28 22:28     ` Kent Overstreet
2012-08-28 23:01       ` Kent Overstreet
2012-08-29  1:31         ` Vivek Goyal
2012-08-29  3:25           ` Kent Overstreet
2012-08-29 12:57             ` Vivek Goyal [this message]
2012-08-29 14:39               ` [dm-devel] " Alasdair G Kergon
2012-08-29 16:26                 ` Kent Overstreet
2012-08-29 21:01                   ` John Stoffel
2012-08-29 21:08                     ` Kent Overstreet
2012-08-28 22:06   ` Vivek Goyal
2012-08-28 22:23     ` Kent Overstreet
2012-08-29 16:24   ` Mikulas Patocka
2012-08-29 16:50     ` Kent Overstreet
2012-08-29 16:57       ` [dm-devel] " Alasdair G Kergon
2012-08-29 17:07       ` Vivek Goyal
2012-08-29 17:13         ` Kent Overstreet
2012-08-29 17:23           ` [dm-devel] " Alasdair G Kergon
2012-08-29 17:32             ` Kent Overstreet
2012-08-30 22:07           ` Vivek Goyal
2012-08-31  1:43             ` Kent Overstreet
2012-08-31  1:55               ` Kent Overstreet
2012-08-31 15:01               ` Vivek Goyal
2012-09-03  1:26                 ` Kent Overstreet
2012-09-03 20:41               ` Mikulas Patocka
2012-09-04  3:41                 ` Kent Overstreet
2012-09-04 18:55                   ` Tejun Heo
2012-09-04 19:01                     ` Tejun Heo
2012-09-04 19:43                       ` Kent Overstreet
2012-09-04 19:42                     ` Kent Overstreet
2012-09-04 21:03                       ` Tejun Heo
2012-09-04 19:26                   ` Mikulas Patocka
2012-09-04 19:39                     ` Vivek Goyal
2012-09-04 19:51                     ` [PATCH] dm: Use bioset's front_pad for dm_target_io Kent Overstreet
2012-09-04 21:20                       ` Tejun Heo
2012-09-11 19:28                       ` [PATCH 2] " Mikulas Patocka
2012-09-11 19:50                         ` Kent Overstreet
2012-09-12 22:31                           ` Mikulas Patocka
2012-09-14 23:09                             ` [dm-devel] " Alasdair G Kergon
2012-09-01  2:13             ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Tejun Heo
2012-09-03  1:34               ` [PATCH v2] " Kent Overstreet
2012-09-04 15:00               ` [PATCH v7 9/9] " Vivek Goyal
2012-09-03  0:49             ` Dave Chinner
2012-09-03  1:17               ` Kent Overstreet
2012-09-04 13:54               ` Vivek Goyal
2012-09-04 18:26                 ` Tejun Heo
2012-09-05  3:57                   ` Dave Chinner
2012-09-05  4:37                     ` Tejun Heo

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