locking/rwsem: Disable preemption in all down_read*() and up_read() code paths
Commit: 91d2a812 ("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. But commit: 48dfb5d2 ("locking/rwsem: Disable preemption while trying for rwsem lock") ... disabled 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: 91d2a812 ("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> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230126003628.365092-3-longman@redhat.com
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