arm64: spinlock: Fix theoretical trylock() A-B-A with LSE atomics
authorWill Deacon <will.deacon@arm.com>
Wed, 31 Jan 2018 12:12:20 +0000 (12:12 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 26 Apr 2018 09:02:17 +0000 (11:02 +0200)
commit4ec317a41d80145de90bd320928da6916572b6f0
tree83e6a9b90a3c321fa0854c4da4201b84f835232f
parent693b9589c297e0b05359f62a6b8dc73289c0e3e4
arm64: spinlock: Fix theoretical trylock() A-B-A with LSE atomics

[ Upstream commit 202fb4ef81e3ec765c23bd1e6746a5c25b797d0e ]

If the spinlock "next" ticket wraps around between the initial LDR
and the cmpxchg in the LSE version of spin_trylock, then we can erroneously
think that we have successfuly acquired the lock because we only check
whether the next ticket return by the cmpxchg is equal to the owner ticket
in our updated lock word.

This patch fixes the issue by performing a full 32-bit check of the lock
word when trying to determine whether or not the CASA instruction updated
memory.

Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/arm64/include/asm/spinlock.h