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[PULL,12/15] cpus: don't use atomic_read for vm_clock_warp_start

Message ID 1459849818-26649-13-git-send-email-pbonzini@redhat.com
State Accepted
Commit ccffff48c93c30733783b05cd1ef843a4c274653
Headers show

Commit Message

Paolo Bonzini April 5, 2016, 9:50 a.m. UTC 
From: Alex Bennée <alex.bennee@linaro.org>


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>

---
 cpus.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

-- 
2.5.5
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Patch

diff --git a/cpus.c b/cpus.c
index 8ae4777..cbeb1f6 100644
--- a/cpus.c
+++ b/cpus.c
@@ -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;
     }