d039f38801
- Plug a race in the lock handoff which is caused by inconsistency of the
reader and writer path and can lead to corruption of the underlying
counter.
- down_read_trylock() is suboptimal when the lock is contended and
multiple readers trylock concurrently. That's due to the initial value
being read non-atomically which results in at least two compare exchange
loops. Making the initial readout atomic reduces this significantly.
Whith 40 readers by 11% in a benchmark which enforces contention on
mmap_sem.
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Merge tag 'locking-urgent-2021-11-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Thomas Gleixner:
"Two regression fixes for reader writer semaphores:
- Plug a race in the lock handoff which is caused by inconsistency of
the reader and writer path and can lead to corruption of the
underlying counter.
- down_read_trylock() is suboptimal when the lock is contended and
multiple readers trylock concurrently. That's due to the initial
value being read non-atomically which results in at least two
compare exchange loops. Making the initial readout atomic reduces
this significantly. Whith 40 readers by 11% in a benchmark which
enforces contention on mmap_sem"
* tag 'locking-urgent-2021-11-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/rwsem: Optimize down_read_trylock() under highly contended case
locking/rwsem: Make handoff bit handling more consistent
Linux kernel
============
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