Messages in this thread | | | Date | Fri, 16 Dec 2022 16:03:16 +0100 | From | Jiri Wiesner <> | Subject | Re: [PATCH v6 2/6] locking/rwsem: Disable preemption at all down_read*() and up_read() code paths |
| |
On Thu, Nov 17, 2022 at 09:20:12PM -0500, Waiman Long wrote: > Commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically > spin on owner") assumes that when the owner field is changed to NULL, > the lock will become free soon. Commit 48dfb5d2560d ("locking/rwsem: > Disable preemption while trying for rwsem lock") disables preemption > when acquiring rwsem for write. However, preemption has not yet been > disabled when acquiring a read lock on a rwsem. So a reader can add a > RWSEM_READER_BIAS to count without setting owner to signal a reader, > got preempted out by a RT task which then spins in the writer slowpath > as owner remains NULL leading to live lock. > > One easy way to fix this problem is to disable preemption at all the > down_read*() and up_read() code paths as implemented in this patch. > > Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner") > Reported-by: Mukesh Ojha <quic_mojha@quicinc.com> > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Waiman Long <longman@redhat.com> > ---
Tested-by: Jiri Wiesner <jwiesner@suse.de>
-- Jiri Wiesner SUSE Labs
| |