K 10
svn:author
V 9
jimharris
K 8
svn:date
V 27
2015-10-30T16:06:34.007995Z
K 7
svn:log
V 1328
nvme: fix race condition in split bio completion path

Fixes race condition observed under following circumstances:

1) I/O split on 128KB boundary with Intel NVMe controller.
   Current Intel controllers produce better latency when
   I/Os do not span a 128KB boundary - even if the I/O size
   itself is less than 128KB.
2) Per-CPU I/O queues are enabled.
3) Child I/Os are submitted on different submission queues.
4) Interrupts for child I/O completions occur almost
   simultaneously.
5) ithread for child I/O A increments bio_inbed, then
   immediately is preempted (rendezvous IPI, higher priority
   interrupt).
6) ithread for child I/O B increments bio_inbed, then completes
   parent bio since all children are now completed.
7) parent bio is freed, and immediately reallocated for a VFS
   or gpart bio (including setting bio_children to 1 and
   clearing bio_driver1).
8) ithread for child I/O A resumes processing.  bio_children
   for what it thinks is the parent bio is set to 1, so it
   thinks it needs to complete the parent bio.

Result is either calling a NULL callback function, or double freeing
the bio to its uma zone.

PR:		203746
Reported by:	Drew Gallatin <gallatin@netflix.com>,
		Marc Goroff <mgoroff@quorum.net>
Tested by:	Drew Gallatin <gallatin@netflix.com>
MFC after:	3 days
Sponsored by:	Intel

END