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block: Mark drain related functions GRAPH_RDLOCK

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Draining recursively traverses the graph, therefore we need to make sure
that also such accesses to the graph are protected by the graph rdlock.

There are 3 different drain callers to consider:
1. drain in the main loop: no issue at all, rdlock is nop.
2. drain in an iothread: rdlock only works in main loop or coroutines,
   so disallow it.
3. drain in a coroutine (regardless of AioContext): the drain mechanism
   takes care of scheduling a BH in the bs->aio_context that will
   then take care of perform the actual draining. This is wrong,
   because as pointed in (2) if bs->aio_context is an iothread then
   rdlock won't work. Therefore change bdrv_co_yield_to_drain to
   schedule the BH in the main loop.

Caller (2) also implies that we need to modify test-bdrv-drain.c to
disallow draining in the iothreads.

For some places, we know that they will hold the lock, but we don't have
the GRAPH_RDLOCK annotations yet. In this case, add assume_graph_lock()
with a FIXME comment. These places will be removed once everything is
properly annotated.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-6-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Emanuele Giuseppe Esposito 2023-09-29 16:51:40 +02:00 • committed by Kevin Wolf
parent 2b3912f135
commit d05ab380db
5 changed files with 54 additions and 17 deletions
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4
tests/unit/test-bdrv-drain.c
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@ -1196,7 +1196,7 @@ static void coroutine_mixed_fn detach_by_parent_aio_cb(void *opaque, int ret)
}
}
static void detach_by_driver_cb_drained_begin(BdrvChild *child)
static void GRAPH_RDLOCK detach_by_driver_cb_drained_begin(BdrvChild *child)
{
struct detach_by_parent_data *data = &detach_by_parent_data;
@ -1233,7 +1233,7 @@ static BdrvChildClass detach_by_driver_cb_class;
* state is messed up, but if it is only polled in the single
* BDRV_POLL_WHILE() at the end of the drain, this should work fine.
*/
static void test_detach_indirect(bool by_parent_cb)
static void TSA_NO_TSA test_detach_indirect(bool by_parent_cb)
{
BlockBackend *blk;
BlockDriverState *parent_a, *parent_b, *a, *b, *c;