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qemu-patch-raspberry4
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block: avoid recursive AioContext acquire in bdrv_inactivate_all() 

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 <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20171207201320.19284-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
stable-2.12
Paolo Bonzini 2017-12-07 20:13:15 +00:00 committed by Stefan Hajnoczi
parent 0a75b60cdb
commit bd6458e410
1 changed files with 11 additions and 3 deletions
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14
block.c
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@ -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;
}