Re: [PATCH] libiscsi: add lock around task lists to fix list corruption regression

["Martin K. Petersen" <martin.petersen-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

>>>>> "Chris" == Chris Leech <cleech-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:

Chris> There's a rather long standing regression from commit 659743b
Chris> [SCSI] libiscsi: Reduce locking contention in fast path

Chris> Depending on iSCSI target behavior, it's possible to hit the case
Chris> in iscsi_complete_task where the task is still on a pending list
Chris> (!list_empty(&task->running)).  When that happens the task is
Chris> removed from the list while holding the session back_lock, but
Chris> other task list modification occur under the frwd_lock.  That
Chris> leads to linked list corruption and eventually a panicked system.

Chris> Rather than back out the session lock split entirely, in order to
Chris> try and keep some of the performance gains this patch adds
Chris> another lock to maintain the task lists integrity.

Chris> Major enterprise supported kernels have been backing out the lock
Chris> split for while now, thanks to the efforts at IBM where a lab
Chris> setup has the most reliable reproducer I've seen on this issue.
Chris> This patch has been tested there successfully.

Reviews, please!

-- 
Martin K. Petersen	Oracle Linux Engineering

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