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Bug 1225189

Summary: librbd: aio calls may block
Product: Red Hat Enterprise Linux 7 Reporter: Josh Durgin <jdurgin>
Component: ceph-commonAssignee: Boris Ranto <branto>
Status: CLOSED DUPLICATE QA Contact: Tamil <tmuthami>
Severity: high Docs Contact:
Priority: unspecified    
Version: 7.2CC: ceph-eng-bugs, ceph-qe-bugs, jdillama
Target Milestone: rc   
Target Release: 7.2   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: 1225171 Environment:
Last Closed: 2015-06-17 18:17:03 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Josh Durgin 2015-05-26 19:03:20 UTC 
+++ This bug was initially created as a clone of Bug #1225171 +++

QEMU runs these from its threads, so blocking here causes the vcpu to lock up from the guest's perspective, resulting in messages in linux guests like

BUG: soft lockup - CPU#1 stuck for 520s!

One cause that has been observed is via Objecter-level throttling of requests:

With caching disabled, this blocks directly in aio_read/write().

With caching enabled, the cache does i/o while holding its lock, and if it is throttled in its flusher thread, for example, readx() and writex() will block waiting on the cache lock.
Comment 2 Boris Ranto 2015-06-17 18:17:03 UTC 
Closing this one, the other bz (1225188) will get cloned once/if it is approved for z-stream.

*** This bug has been marked as a duplicate of bug 1225188 ***