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e2e74d617e
We have found a race in the optimisation used in the dm cache writethrough implementation. Currently, dm core sends the cache target two bios, one for the origin device and one for the cache device and these are processed in parallel. This patch avoids the race by changing the code back to a simpler (slower) implementation which processes the two writes in series, one after the other, until we can develop a complete fix for the problem. When the cache is in writethrough mode it needs to send WRITE bios to both the origin and cache devices. Previously we've been implementing this by having dm core query the cache target on every write to find out how many copies of the bio it wants. The cache will ask for two bios if the block is in the cache, and one otherwise. Then main problem with this is it's racey. At the time this check is made the bio hasn't yet been submitted and so isn't being taken into account when quiescing a block for migration (promotion or demotion). This means a single bio may be submitted when two were needed because the block has since been promoted to the cache (catastrophic), or two bios where only one is needed (harmless). I really don't want to start entering bios into the quiescing system (deferred_set) in the get_num_write_bios callback. Instead this patch simplifies things; only one bio is submitted by the core, this is first written to the origin and then the cache device in series. Obviously this will have a latency impact. deferred_writethrough_bios is introduced to record bios that must be later issued to the cache device from the worker thread. This deferred submission, after the origin bio completes, is required given that we're in interrupt context (writethrough_endio). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> |
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| .. | ||
| persistent-data | ||
| bitmap.c | ||
| bitmap.h | ||
| dm-bio-prison.c | ||
| dm-bio-prison.h | ||
| dm-bio-record.h | ||
| dm-bufio.c | ||
| dm-bufio.h | ||
| dm-cache-block-types.h | ||
| dm-cache-metadata.c | ||
| dm-cache-metadata.h | ||
| dm-cache-policy-cleaner.c | ||
| dm-cache-policy-internal.h | ||
| dm-cache-policy-mq.c | ||
| dm-cache-policy.c | ||
| dm-cache-policy.h | ||
| dm-cache-target.c | ||
| dm-crypt.c | ||
| dm-delay.c | ||
| dm-exception-store.c | ||
| dm-exception-store.h | ||
| dm-flakey.c | ||
| dm-io.c | ||
| dm-ioctl.c | ||
| dm-kcopyd.c | ||
| dm-linear.c | ||
| dm-log-userspace-base.c | ||
| dm-log-userspace-transfer.c | ||
| dm-log-userspace-transfer.h | ||
| dm-log.c | ||
| dm-mpath.c | ||
| dm-mpath.h | ||
| dm-path-selector.c | ||
| dm-path-selector.h | ||
| dm-queue-length.c | ||
| dm-raid.c | ||
| dm-raid1.c | ||
| dm-region-hash.c | ||
| dm-round-robin.c | ||
| dm-service-time.c | ||
| dm-snap-persistent.c | ||
| dm-snap-transient.c | ||
| dm-snap.c | ||
| dm-stripe.c | ||
| dm-sysfs.c | ||
| dm-table.c | ||
| dm-target.c | ||
| dm-thin-metadata.c | ||
| dm-thin-metadata.h | ||
| dm-thin.c | ||
| dm-uevent.c | ||
| dm-uevent.h | ||
| dm-verity.c | ||
| dm-zero.c | ||
| dm.c | ||
| dm.h | ||
| faulty.c | ||
| Kconfig | ||
| linear.c | ||
| linear.h | ||
| Makefile | ||
| md.c | ||
| md.h | ||
| multipath.c | ||
| multipath.h | ||
| raid1.c | ||
| raid1.h | ||
| raid5.c | ||
| raid5.h | ||
| raid10.c | ||
| raid10.h | ||
| raid0.c | ||
| raid0.h | ||