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edu: add smp_mb__after_rmw()

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Ensure ordering between clearing the COMPUTING flag and checking
IRQFACT, and between setting the IRQFACT flag and checking
COMPUTING.  This ensures that no wakeups are lost.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2023-03-02 11:16:13 +01:00
parent 6c5df4b48f
commit 2482aeea41
1 changed files with 5 additions and 0 deletions
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5
hw/misc/edu.c
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@ -267,6 +267,8 @@ static void edu_mmio_write(void *opaque, hwaddr addr, uint64_t val,
case 0x20:
if (val & EDU_STATUS_IRQFACT) {
qatomic_or(&edu->status, EDU_STATUS_IRQFACT);
/* Order check of the COMPUTING flag after setting IRQFACT. */
smp_mb__after_rmw();
} else {
qatomic_and(&edu->status, ~EDU_STATUS_IRQFACT);
}
@ -349,6 +351,9 @@ static void *edu_fact_thread(void *opaque)
qemu_mutex_unlock(&edu->thr_mutex);
qatomic_and(&edu->status, ~EDU_STATUS_COMPUTING);
/* Clear COMPUTING flag before checking IRQFACT. */
smp_mb__after_rmw();
if (qatomic_read(&edu->status) & EDU_STATUS_IRQFACT) {
qemu_mutex_lock_iothread();
edu_raise_irq(edu, FACT_IRQ);