Commit aa1361d5 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

block: Add missing locking in bdrv_co_drain_bh_cb() 



bdrv_do_drained_begin/end() assume that they are called with the
AioContext lock of bs held. If we call drain functions from a coroutine
with the AioContext lock held, we yield and schedule a BH to move out of
coroutine context. This means that the lock for the home context of the
coroutine is released and must be re-acquired in the bottom half.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
parent ae23dde9

block/io.c

+15 −0
Original line number Diff line number Diff line
@@ -288,6 +288,18 @@ static void bdrv_co_drain_bh_cb(void *opaque) 
    BlockDriverState *bs = data->bs;



    if (bs) {

        AioContext *ctx = bdrv_get_aio_context(bs);

        AioContext *co_ctx = qemu_coroutine_get_aio_context(co);



        /*

         * When the coroutine yielded, the lock for its home context was

         * released, so we need to re-acquire it here. If it explicitly

         * acquired a different context, the lock is still held and we don't

         * want to lock it a second time (or AIO_WAIT_WHILE() would hang).

         */

        if (ctx == co_ctx) {

            aio_context_acquire(ctx);

        }

        bdrv_dec_in_flight(bs);

        if (data->begin) {

            bdrv_do_drained_begin(bs, data->recursive, data->parent,
@@ -296,6 +308,9 @@ static void bdrv_co_drain_bh_cb(void *opaque) 
            bdrv_do_drained_end(bs, data->recursive, data->parent,

                                data->ignore_bds_parents);

        }

        if (ctx == co_ctx) {

            aio_context_release(ctx);

        }

    } else {

        assert(data->begin);

        bdrv_drain_all_begin();

include/qemu/coroutine.h

+5 −0
Original line number Diff line number Diff line
@@ -89,6 +89,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co); 
 */

void coroutine_fn qemu_coroutine_yield(void);



/**

 * Get the AioContext of the given coroutine

 */

AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);



/**

 * Get the currently executing coroutine

 */

util/qemu-coroutine.c

+5 −0
Original line number Diff line number Diff line
@@ -198,3 +198,8 @@ bool qemu_coroutine_entered(Coroutine *co) 
{

    return co->caller;

}



AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)

{

    return co->ctx;

}