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[Qemu-block] [PATCH v2 1/6] block: avoid recursive AioContext acquire in
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-block] [PATCH v2 1/6] block: avoid recursive AioContext acquire in bdrv_inactivate_all() |
Date: |
Thu, 7 Dec 2017 20:13:15 +0000 |
From: Paolo Bonzini <address@hidden>
BDRV_POLL_WHILE() does not support recursive AioContext locking. It
only releases the AioContext lock once regardless of how many times the
caller has acquired it. This results in a hang since the IOThread does
not make progress while the AioContext is still locked.
The following steps trigger the hang:
$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
-object iothread,id=iothread0 \
-device virtio-scsi-pci,iothread=iothread0 \
-drive if=none,id=drive0,file=test.img,format=raw \
-device scsi-hd,drive=drive0 \
-drive if=none,id=drive1,file=test.img,format=raw \
-device scsi-hd,drive=drive1
$ qemu-system-x86_64 ...same options... \
-incoming tcp::1234
(qemu) migrate tcp:127.0.0.1:1234
...hang...
Tested-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
block.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/block.c b/block.c
index 9a1a0d1e73..1c37ce4554 100644
--- a/block.c
+++ b/block.c
@@ -4320,9 +4320,15 @@ int bdrv_inactivate_all(void)
BdrvNextIterator it;
int ret = 0;
int pass;
+ GSList *aio_ctxs = NULL, *ctx;
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
- aio_context_acquire(bdrv_get_aio_context(bs));
+ AioContext *aio_context = bdrv_get_aio_context(bs);
+
+ if (!g_slist_find(aio_ctxs, aio_context)) {
+ aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
+ aio_context_acquire(aio_context);
+ }
}
/* We do two passes of inactivation. The first pass calls to drivers'
@@ -4340,9 +4346,11 @@ int bdrv_inactivate_all(void)
}
out:
- for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
- aio_context_release(bdrv_get_aio_context(bs));
+ for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
+ AioContext *aio_context = ctx->data;
+ aio_context_release(aio_context);
}
+ g_slist_free(aio_ctxs);
return ret;
}
--
2.14.3
- [Qemu-block] [PATCH v2 0/6] block: avoid recursive AioContext acquire in bdrv_inactivate_all(), Stefan Hajnoczi, 2017/12/07
- [Qemu-block] [PATCH v2 2/6] docs: mark nested AioContext locking as a legacy API, Stefan Hajnoczi, 2017/12/07
- [Qemu-block] [PATCH v2 1/6] block: avoid recursive AioContext acquire in bdrv_inactivate_all(),
Stefan Hajnoczi <=
- [Qemu-block] [PATCH v2 3/6] blockdev: add x-blockdev-set-iothread force boolean, Stefan Hajnoczi, 2017/12/07
- [Qemu-block] [PATCH v2 4/6] iotests: add VM.add_object(), Stefan Hajnoczi, 2017/12/07
- [Qemu-block] [PATCH v2 5/6] iothread: fix iothread_stop() race condition, Stefan Hajnoczi, 2017/12/07
- [Qemu-block] [PATCH v2 6/6] qemu-iotests: add 203 savevm with IOThreads test, Stefan Hajnoczi, 2017/12/07
- Re: [Qemu-block] [PATCH v2 0/6] block: avoid recursive AioContext acquire in bdrv_inactivate_all(), Paolo Bonzini, 2017/12/13