From: Greg Kurz <[email protected]>
Since commit "60253ed1e6ec rng: add request queue support to rng-random",
the use of a spapr_rng device may hang vCPU threads.
The following path is taken without holding the lock to the main loop mutex:
h_random()
rng_backend_request_entropy()
rng_random_request_entropy()
qemu_set_fd_handler()
The consequence is that entropy_available() may be called before the vCPU
thread could even queue the request: depending on the scheduling, it may
happen that entropy_available() does not call random_recv()->qemu_sem_post().
The vCPU thread will then sleep forever in h_random()->qemu_sem_wait().
This could not happen before 60253ed1e6ec because entropy_available() used
to call random_recv() unconditionally.
This patch ensures the lock is held to avoid the race.
Signed-off-by: Greg Kurz <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Signed-off-by: David Gibson <[email protected]>
---
hw/ppc/spapr_rng.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/hw/ppc/spapr_rng.c b/hw/ppc/spapr_rng.c
index a39d472..02d6be4 100644
--- a/hw/ppc/spapr_rng.c
+++ b/hw/ppc/spapr_rng.c
@@ -77,13 +77,13 @@ static target_ulong h_random(PowerPCCPU *cpu,
sPAPRMachineState *spapr,
hrdata.val.v64 = 0;
hrdata.received = 0;
- qemu_mutex_unlock_iothread();
while (hrdata.received < 8) {
rng_backend_request_entropy(rngstate->backend, 8 - hrdata.received,
random_recv, &hrdata);
+ qemu_mutex_unlock_iothread();
qemu_sem_wait(&hrdata.sem);
+ qemu_mutex_lock_iothread();
}
- qemu_mutex_lock_iothread();
qemu_sem_destroy(&hrdata.sem);
args[0] = hrdata.val.v64;
--
2.5.0
