tree cea1890c9070f4edd6ac3e8811ba4cdb1499e410
parent f8132d62a2deedca1b7558028cfe72f93ad5ba2d
parent 14c24048841151548a3f4d9e218510c844c1b737
author Linus Torvalds <torvalds@linux-foundation.org> 1638119081 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1638119081 -0800
mergetag object 14c24048841151548a3f4d9e218510c844c1b737
 type commit
 tag locking-urgent-2021-11-28
 tagger Thomas Gleixner <tglx@linutronix.de> 1638116626 +0100
 
 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.
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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