On Fri, Mar 11, 2016 at 07:48:47PM +0100, Greg Kurz wrote: > 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 <gk...@linux.vnet.ibm.com>
Applied to ppc-for-2.6 > --- > > Thomas, > > This is the problem mentioned by Cedric in: > > https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg02526.html > > Cheers. > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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