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scsi: fix device removal race vs IO restart callback on resume 

There is (mostly theoretical) race between removal of a scsi device and
scsi_dma_restart_bh.

It used to be easier to hit this race prior to my / Paulo's patch series
that added rcu to scsi bus device handling code, but IMHO this race
should still be possible to hit, at least in theory.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1854811

Fix it anyway with a patch that was proposed by Paulo in the above bugzilla.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201210125929.1136390-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2020-12-10 14:59:29 +02:00 committed by Paolo Bonzini
parent 835cbd8d44
commit cfd4e36352
1 changed files with 4 additions and 0 deletions
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4
hw/scsi/scsi-bus.c
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@ -170,6 +170,8 @@ static void scsi_dma_restart_bh(void *opaque)
scsi_req_unref(req);
}
aio_context_release(blk_get_aio_context(s->conf.blk));
/* Drop the reference that was acquired in scsi_dma_restart_cb */
object_unref(OBJECT(s));
}
void scsi_req_retry(SCSIRequest *req)
@ -188,6 +190,8 @@ static void scsi_dma_restart_cb(void *opaque, int running, RunState state)
}
if (!s->bh) {
AioContext *ctx = blk_get_aio_context(s->conf.blk);
/* The reference is dropped in scsi_dma_restart_bh.*/
object_ref(OBJECT(s));
s->bh = aio_bh_new(ctx, scsi_dma_restart_bh, s);
qemu_bh_schedule(s->bh);
}