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wait_on_bit: add an acquire memory barrier

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There are several places in the kernel where wait_on_bit is not followed
by a memory barrier (for example, in drivers/md/dm-bufio.c:new_read).

On architectures with weak memory ordering, it may happen that memory
accesses that follow wait_on_bit are reordered before wait_on_bit and
they may return invalid data.

Fix this class of bugs by introducing a new function "test_bit_acquire"
that works like test_bit, but has acquire memory ordering semantics.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mikulas Patocka
2022-08-26 09:17:08 -04:00
committed by Linus Torvalds
parent 4c612826be
commit 8238b45798
10 changed files with 60 additions and 12 deletions
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1
include/linux/bitops.h
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@@ -59,6 +59,7 @@ extern unsigned long __sw_hweight64(__u64 w);
#define __test_and_clear_bit(nr, addr) bitop(___test_and_clear_bit, nr, addr)
#define __test_and_change_bit(nr, addr) bitop(___test_and_change_bit, nr, addr)
#define test_bit(nr, addr) bitop(_test_bit, nr, addr)
#define test_bit_acquire(nr, addr) bitop(_test_bit_acquire, nr, addr)
/*
* Include this here because some architectures need generic_ffs/fls in