mbox series

[v4,0/6] blkdebug: fix racing condition when iterating on

Message ID 20210604100741.18966-1-eesposit@redhat.com
Headers show
Series blkdebug: fix racing condition when iterating on | expand

Message

Emanuele Giuseppe Esposito June 4, 2021, 10:07 a.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 5-6 are somewhat independent of the others, patch 5 removes the need
of new_state field, and patch 6 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>
---
v4:
* Patch 5 (new): get rid of new_state and instead use a local variable
* Patch 6: move the state update inside the same guard lock where the new
  one is decided, to have a single critical section and avoid use-before-update. 

Emanuele Giuseppe Esposito (6):
  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
  block/blkdebug: remove new_state field and instead use a local
    variable
  blkdebug: protect rules and suspended_reqs with a lock

 block/blkdebug.c | 128 +++++++++++++++++++++++++++++++----------------
 1 file changed, 84 insertions(+), 44 deletions(-)