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2e5b887cfc
Even if the caller has both the old and the new AioContext's, there can
be a deadlock, due to the leading bdrv_drain_all.
Suppose there are four io threads (A, B, A0, B0) with A and B owning a
BDS for each (bs_a, bs_b); Now A wants to move bs_a to iothread A0, and
B wants to move bs_b to B0, at the same time:
iothread A iothread B
--------------------------------------------------------------------------
aio_context_acquire(A0) /* OK */ aio_context_acquire(B0) /* OK */
bdrv_set_aio_context(bs_a, A0) bdrv_set_aio_context(bs_b, B0)
-> bdrv_drain_all() -> bdrv_drain_all()
-> acquire A /* OK */ -> acquire A /* blocked */
-> acquire B /* blocked */ -> acquire B
... ...
Deadlock happens because A is waiting for B, and B is waiting for A.
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1423969591-23646-2-git-send-email-famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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| block | ||
| disas | ||
| exec | ||
| fpu | ||
| hw | ||
| libdecnumber | ||
| migration | ||
| monitor | ||
| net | ||
| qapi | ||
| qemu | ||
| qom | ||
| sysemu | ||
| ui | ||
| config.h | ||
| elf.h | ||
| glib-compat.h | ||
| qemu-common.h | ||
| qemu-io.h | ||
| qjson.h | ||
| trace-tcg.h | ||
| trace.h | ||