The memory barrier usage in updating the random ptr hash for %p in

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vsprintf is incorrect. Instead of adding the read memory barrier
 into vsprintf() which will cause a slight degradation to a commonly
 used function in the kernel just to solve a very unlikely race
 condition that can only happen at boot up, change the code from
 using a variable branch to a static_branch. Not only does this solve
 the race condition, it actually will improve the performance of
 vsprintf() by removing the conditional branch that is only needed
 at boot.
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Merge tag 'trace-v4.17-rc5-vsprintf' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull memory barrier for from Steven Rostedt:
 "The memory barrier usage in updating the random ptr hash for %p in
  vsprintf is incorrect.

  Instead of adding the read memory barrier into vsprintf() which will
  cause a slight degradation to a commonly used function in the kernel
  just to solve a very unlikely race condition that can only happen at
  boot up, change the code from using a variable branch to a
  static_branch.

  Not only does this solve the race condition, it actually will improve
  the performance of vsprintf() by removing the conditional branch that
  is only needed at boot"

* tag 'trace-v4.17-rc5-vsprintf' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  vsprintf: Replace memory barrier with static_key for random_ptr_key update

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This commit is contained in:

Linus Torvalds 2018-05-16 11:02:54 -07:00

parent 21b9f1c7e3 85f4f12d51

commit 9d38cd06c3

1 changed files with 15 additions and 11 deletions

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lib/vsprintf.c

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