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MFC r304184:

Description

MFC r304184:

sem_post(): wake up the sleeper only after adjusting has_waiters

If the caller of sem_post() wakes up a thread sleeping via sem_wait()
before it clears the has_waiters flag, the caller of sem_wait() has no way of
knowing when it is safe to destroy the semaphore and reuse the memory. This is
because the caller of sem_post() may be interrupted between the wake step and
the clearing of has_waiters. It will then write into the has_waiters flag in
userspace after being preempted for some unknown amount of time.

Approved by: vangyzen (mentor)
Sponsored by: Dell Inc.

Details

Committed
badgerAug 30 2016, 1:39 PM
Parents
rS305062: Add an 'Important Notes' section before the 'Upgrading' section.
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