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[v3,0/5] blkdebug: fix racing condition when iterating on

Message ID 20210517145049.55268-1-eesposit@redhat.com (mailing list archive)
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Series blkdebug: fix racing condition when iterating on | expand

Message

Emanuele Giuseppe Esposito May 17, 2021, 2:50 p.m. UTC 
When qemu_coroutine_enter is executed in a loop
(even QEMU_FOREACH_SAFE), the new routine can modify the list,
for example removing an element, causing problem when control
is given back to the caller that continues iterating on the same list. 

Patch 1 solves the issue in blkdebug_debug_resume by restarting
the list walk after every coroutine_enter if list has to be fully iterated.
Patches 2,3,4 aim to fix blkdebug_debug_event by gathering
all actions that the rules make in a counter and invoking 
the respective coroutine_yeld only after processing all requests.

Patch 5 is somewhat independent of the others, it adds a lock to
protect rules and suspended_reqs; right now everything works because
it's protected by the AioContext lock.
This is a preparation for the current proposal of removing the AioContext
lock and instead using smaller granularity locks to allow multiple
iothread execution in the same block device.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
v2 -> v3
* Fix "yeld"->"yield" in patches 3-4 [Eric]
* Use lock guard instead of lock/unlock in patch 5 [Eric]

Emanuele Giuseppe Esposito (5):
  blkdebug: refactor removal of a suspended request
  blkdebug: move post-resume handling to resume_req_by_tag
  blkdebug: track all actions
  blkdebug: do not suspend in the middle of QLIST_FOREACH_SAFE
  blkdebug: protect rules and suspended_reqs with a lock

 block/blkdebug.c | 124 +++++++++++++++++++++++++++++++----------------
 1 file changed, 83 insertions(+), 41 deletions(-)