diff mbox series

[PULL,1/1] icount: Take iothread lock when running QEMU timers

Message ID 20220809121307.560286-2-peter.maydell@linaro.org
State Accepted
Commit c7f26ded6d5065e4116f630f6a490b55f6c5f58e
Headers show
Series [PULL,1/1] icount: Take iothread lock when running QEMU timers | expand

Commit Message

Peter Maydell Aug. 9, 2022, 12:13 p.m. UTC 
The function icount_prepare_for_run() is called with the iothread
unlocked, but it can call icount_notify_aio_contexts() which will
run qemu timer handlers. Those are supposed to be run only with
the iothread lock held, so take the lock while we do that.

Since icount mode runs everything on a single thread anyway,
not holding the lock is likely mostly not going to introduce
races, but it can cause us to trip over assertions that we
do hold the lock, such as the one reported in issue 1130.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1130
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-id: 20220801164527.3134765-1-peter.maydell@linaro.org
---
 accel/tcg/tcg-accel-ops-icount.c | 6 ++++++
 1 file changed, 6 insertions(+)
diff mbox series

Patch

diff --git a/accel/tcg/tcg-accel-ops-icount.c b/accel/tcg/tcg-accel-ops-icount.c
index 8f1dda4344c..84cc7421be8 100644
--- a/accel/tcg/tcg-accel-ops-icount.c
+++ b/accel/tcg/tcg-accel-ops-icount.c
@@ -109,7 +109,13 @@  void icount_prepare_for_run(CPUState *cpu)
     replay_mutex_lock();
 
     if (cpu->icount_budget == 0) {
+        /*
+         * We're called without the iothread lock, so must take it while
+         * we're calling timer handlers.
+         */
+        qemu_mutex_lock_iothread();
         icount_notify_aio_contexts();
+        qemu_mutex_unlock_iothread();
     }
 }