From 9f02cfc84b85929947b32fe1674fbc6a429f332a Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 2 Dec 2014 11:23:14 +0000 Subject: bitmap: add atomic set functions Use atomic_or() for atomic bitmaps where several threads may set bits at the same time. This avoids the race condition between threads loading an element, bitwise ORing, and then storing the element. When setting all bits in a word we can avoid atomic ops and instead just use an smp_mb() at the end. Most bitmap users don't need atomicity so introduce new functions. Signed-off-by: Stefan Hajnoczi Message-Id: <1417519399-3166-2-git-send-email-stefanha@redhat.com> [Avoid barrier in the single word case, use full barrier instead of write. - Paolo] Reviewed-by: Fam Zheng Signed-off-by: Paolo Bonzini --- include/qemu/bitops.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/qemu/bitops.h') diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h index 8abdcf9077..8164225152 100644 --- a/include/qemu/bitops.h +++ b/include/qemu/bitops.h @@ -16,6 +16,7 @@ #include #include "host-utils.h" +#include "atomic.h" #define BITS_PER_BYTE CHAR_BIT #define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE) @@ -38,6 +39,19 @@ static inline void set_bit(long nr, unsigned long *addr) *p |= mask; } +/** + * set_bit_atomic - Set a bit in memory atomically + * @nr: the bit to set + * @addr: the address to start counting from + */ +static inline void set_bit_atomic(long nr, unsigned long *addr) +{ + unsigned long mask = BIT_MASK(nr); + unsigned long *p = addr + BIT_WORD(nr); + + atomic_or(p, mask); +} + /** * clear_bit - Clears a bit in memory * @nr: Bit to clear -- cgit 1.4.1