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>
Wed, 30 May 2018 05:50:25 +0000 (07:50 +0200)
commit0675ec13c63f9eb918342b63614738767ef079a3
tree9d40f1365c9f80ea223c352576eb45d848d1963d
parenta0138dc31d07220a07adbf065bb8fee023a02f40
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