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cpus: don't use atomic_read for vm_clock_warp_start 

As vm_clock_warp_start is a 64 bit value this causes problems for the
compiler trying to come up with a suitable atomic operation on 32 bit
hosts. Because the variable is protected by vm_clock_seqlock, we check its
value inside a seqlock critical section.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <1459780549-12942-2-git-send-email-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alex Bennée 2016-04-04 15:35:48 +01:00 committed by Paolo Bonzini
parent a89ef0c357
commit ccffff48c9
1 changed files with 9 additions and 1 deletions
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10
cpus.c
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@ -338,10 +338,18 @@ static int64_t qemu_icount_round(int64_t count)
static void icount_warp_rt(void)
{
unsigned seq;
int64_t warp_start;
/* The icount_warp_timer is rescheduled soon after vm_clock_warp_start
* changes from -1 to another value, so the race here is okay.
*/
if (atomic_read(&vm_clock_warp_start) == -1) {
do {
seq = seqlock_read_begin(&timers_state.vm_clock_seqlock);
warp_start = vm_clock_warp_start;
} while (seqlock_read_retry(&timers_state.vm_clock_seqlock, seq));
if (warp_start == -1) {
return;
}