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authorStefan Hajnoczi <stefanha@redhat.com>2018-03-22 15:28:33 +0000
committerStefan Hajnoczi <stefanha@redhat.com>2018-03-27 13:05:28 +0100
commitc40a2545700e9ad2ef67d5972484bbee4c83b2a6 (patch)
tree2c550ddaf9a59a58c3c07e40c02aded945384cd1 /block
parent67a74148d8828f611fc5a7a23277b8eceb4c9430 (diff)
coroutine: avoid co_queue_wakeup recursion
qemu_aio_coroutine_enter() is (indirectly) called recursively when processing co_queue_wakeup. This can lead to stack exhaustion. This patch rewrites co_queue_wakeup in an iterative fashion (instead of recursive) with bounded memory usage to prevent stack exhaustion. qemu_co_queue_run_restart() is inlined into qemu_aio_coroutine_enter() and the qemu_coroutine_enter() call is turned into a loop to avoid recursion. There is one change that is worth mentioning: Previously, when coroutine A queued coroutine B, qemu_co_queue_run_restart() entered coroutine B from coroutine A. If A was terminating then it would still stay alive until B yielded. After this patch B is entered by A's parent so that a A can be deleted immediately if it is terminating. It is safe to make this change since B could never interact with A if it was terminating anyway. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Message-id: 20180322152834.12656-3-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'block')
-rw-r--r--block/io.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/block/io.c b/block/io.c
index 2b09c656d0..bd9a19a9c4 100644
--- a/block/io.c
+++ b/block/io.c
@@ -249,8 +249,7 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
BdrvCoDrainData data;
/* Calling bdrv_drain() from a BH ensures the current coroutine yields and
- * other coroutines run if they were queued from
- * qemu_co_queue_run_restart(). */
+ * other coroutines run if they were queued by aio_co_enter(). */
assert(qemu_in_coroutine());
data = (BdrvCoDrainData) {