arm64: futex: Bound number of LDXR/STXR loops in FUTEX_WAKE_OP

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Our futex implementation makes use of LDXR/STXR loops to perform atomic
updates to user memory from atomic context. This can lead to latency
problems if we end up spinning around the LL/SC sequence at the expense
of doing something useful.

Rework our futex atomic operations so that we return -EAGAIN if we fail
to update the futex word after 128 attempts. The core futex code will
reschedule if necessary and we'll try again later.

Cc: <stable@kernel.org>
Fixes: 6170a97460 ("arm64: Atomic operations")
Signed-off-by: Will Deacon <will.deacon@arm.com>

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Will Deacon 2019-04-08 14:23:17 +01:00

parent 6b4f4bc9cb

commit 03110a5cb2

1 changed files with 34 additions and 21 deletions

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arch/arm64/include/asm/futex.h

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