Commit bd6458e4 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Stefan Hajnoczi
Browse files

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: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Message-id: 20171207201320.19284-2-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 0a75b60c

block.c

+11 −3
Original line number Diff line number Diff line
@@ -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;

}