Changes from the last version[1] - BLK_EH_RESET_TIMER handling fixed. - s/request->gstate_seqc/request->gstate_seq/ - READ_ONCE() added to blk_mq_rq_udpate_state(). - Removed left over blk_clear_rq_complete() invocation from blk_mq_rq_timed_out(). Currently, blk-mq timeout path synchronizes against the usual issue/completion path using a complex scheme involving atomic bitflags, REQ_ATOM_*, memory barriers and subtle memory coherence rules. Unfortunatley, it contains quite a few holes. It's pretty easy to make blk_mq_check_expired() terminate a later instance of a request. If we induce 5 sec delay before time_after_eq() test in blk_mq_check_expired(), shorten the timeout to 2s, and issue back-to-back large IOs, blk-mq starts timing out requests spuriously pretty quickly. Nothing actually timed out. It just made the call on a recycle instance of a request and then terminated a later instance long after the original instance finished. The scenario isn't theoretical either. This patchset replaces the broken synchronization mechanism with a RCU and generation number based one. Please read the patch description of the second path for more details. This patchset contains the following six patches. 0001-blk-mq-protect-completion-path-with-RCU.patch 0002-blk-mq-replace-timeout-synchronization-with-a-RCU-an.patch 0003-blk-mq-use-blk_mq_rq_state-instead-of-testing-REQ_AT.patch 0004-blk-mq-make-blk_abort_request-trigger-timeout-path.patch 0005-blk-mq-remove-REQ_ATOM_COMPLETE-usages-from-blk-mq.patch 0006-blk-mq-remove-REQ_ATOM_STARTED.patch and is available in the following git branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git blk-mq-timeout diffstat follows. Thanks. block/blk-core.c | 2 block/blk-mq-debugfs.c | 4 block/blk-mq.c | 255 ++++++++++++++++++++++++++++--------------------- block/blk-mq.h | 48 ++++++++- block/blk-timeout.c | 9 - block/blk.h | 7 - include/linux/blk-mq.h | 1 include/linux/blkdev.h | 23 ++++ 8 files changed, 226 insertions(+), 123 deletions(-) -- tejun [1] http://lkml.kernel.org/r/20171209192525.982030-1-tj@xxxxxxxxxx
