tree 4f235e9eacd5a86110b70c39fa21673bb2916946
parent d592a9969141e67a3874c808999a4db4bf82ed83
author hui jiao <simonjiaoh@gmail.com> 1401939264 +0800
committer NeilBrown <neilb@suse.de> 1401952699 +1000

md/raid5: deadlock between retry_aligned_read with barrier io

A chunk aligned read increases counter active_aligned_reads and
decreases it after sub-device handle it successfully. But when a read
error occurs,  the read redispatched by raid5d, and the
active_aligned_reads will not be decreased until we can grab a stripe
head in retry_aligned_read. Now suppose, a barrier io comes, set
conf->quiesce to 2, and wait until both active_stripes and
active_aligned_reads are zero. The retried chunk aligned read gets
stuck at get_active_stripe waiting until conf->quiesce becomes 0.
Retry_aligned_read and barrier io are waiting each other now.
One possible solution is that we ignore conf->quiesce, let the retried
aligned read finish. I reproduced this deadlock and test this patch on
centos6.0

Signed-off-by: NeilBrown <neilb@suse.de>