Am 18.07.2018 um 23:07 hat Michael Roth geschrieben: > Quoting Kevin Wolf (2018-05-29 15:19:17) > > Am 28.05.2018 um 14:03 hat Greg Kurz geschrieben: > > > Removing a drive with drive_del while it is being used to run an I/O > > > intensive workload can cause QEMU to crash. > > > > > > An AIO flush can yield at some point: > > > > > > blk_aio_flush_entry() > > > blk_co_flush(blk) > > > bdrv_co_flush(blk->root->bs) > > > ... > > > qemu_coroutine_yield() > > > > > > and let the HMP command to run, free blk->root and give control > > > back to the AIO flush: > > > > > > hmp_drive_del() > > > blk_remove_bs() > > > bdrv_root_unref_child(blk->root) > > > child_bs = blk->root->bs > > > bdrv_detach_child(blk->root) > > > bdrv_replace_child(blk->root, NULL) > > > blk->root->bs = NULL > > > g_free(blk->root) <============== blk->root becomes stale > > > bdrv_unref(child_bs) > > > bdrv_delete(child_bs) > > > bdrv_close() > > > bdrv_drained_begin() > > > bdrv_do_drained_begin() > > > bdrv_drain_recurse() > > > aio_poll() > > > ... > > > qemu_coroutine_switch() > > > > > > and the AIO flush completion ends up dereferencing blk->root: > > > > > > blk_aio_complete() > > > scsi_aio_complete() > > > blk_get_aio_context(blk) > > > bs = blk_bs(blk) > > > ie, bs = blk->root ? blk->root->bs : NULL > > > ^^^^^ > > > stale > > > > > > The problem is that we should avoid making block driver graph > > > changes while we have in-flight requests. Let's drain all I/O > > > for this BB before calling bdrv_root_unref_child(). > > > > > > Signed-off-by: Greg Kurz <gr...@kaod.org> > > > > Hmm... It sounded convincing, but 'make check-tests/test-replication' > > fails now. The good news is that with the drain fixes, for which I sent > > v2 today, it passes, so instead of staging it in my block branch, I'll > > put it at the end of my branch for the drain fixes. > > > > Might take a bit longer than planned until it's in master, sorry. > > I'm getting the below test-replication failure/trace trying to backport > this patch for 2.12.1 (using this tree: > https://github.com/mdroth/qemu/commits/stable-2.12-staging-f45280cbf) > > Is this the same issue you saw, and if so, are the drain fixes > appropriate for 2.12.x? Are there other prereqs/follow-ups you're > aware of that would also be needed?
I'm not completely sure any more, but yes, I think this might have been the one. My rework of the bdrv_drain_*() functions fixed quite a few bugs, including this one, but the work done since 2.12 is two rather long and quite intrusive series, so I'm not sure if backporting them for 2.12.1 is a good idea. Kevin
