From: Hugh Dickins <hughd@google.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Kent Overstreet <kmo@daterainc.com>, Shaohua Li <shli@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: next bio iters break discard?
Date: Sun, 12 Jan 2014 19:52:40 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.11.1401121909160.1239@eggly.anvils> (raw)
When I try to exercise heavy swapping with discard on mmotm 2014-01-09,
I soon hit a NULL pointer dereference in __blk_recalc_rq_segments():
__blk_recalc_rq_segments
blk_recount_segments
ll_back_merge_fn
bio_attempt_back_merge
blk_queue_bio
generic_make_request
submit_bio
blkdev_issue_discard
swap_do_scheduled_discard
scan_swap_map_try_ssd_cluster
scan_swap_map
get_swap_page
add_to_swap
shrink_page_list
etc. etc.
The crash is on the NULL struct page pointer in page_to_pfn(bv.bv_page)
on line 35 of block/blk-merge.c.
The code around there is not very different from 3.13-rc8 (which doesn't
crash), and I didn't notice REQ_DISCARD or bio_has_data() checks removed.
I think it worked before because the old bio_for_each_segment()
iterator was a straightforward "i < bio->bi_vcnt" loop which would
do nothing when bi_vcnt is 0; but the new iterators are relying
(perhaps) on bio->bi_iter.bi_size which is non-0 despite no data?
I expect it would crash in the same way on other recent nexts and
mmotms, I've not tried.
Hugh
next reply other threads:[~2014-01-13 3:53 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-13 3:52 Hugh Dickins [this message]
2014-01-14 2:33 ` next bio iters break discard? Kent Overstreet
2014-01-14 4:06 ` Martin K. Petersen
2014-01-14 4:48 ` Kent Overstreet
2014-01-14 20:17 ` Martin K. Petersen
2014-01-14 22:24 ` Kent Overstreet
2014-01-16 1:39 ` Martin K. Petersen
2014-01-16 20:21 ` Hugh Dickins
2014-01-17 1:06 ` Kent Overstreet
2014-01-17 1:21 ` Kent Overstreet
2014-01-31 17:17 ` Hugh Dickins
2014-01-31 21:58 ` Jens Axboe
2014-02-04 10:17 ` [PATCH] block: Explicitly handle discard/write same segments Kent Overstreet
2014-02-04 12:25 ` Hugh Dickins
2014-02-04 12:35 ` Kent Overstreet
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