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| Filename | Latest commit message | Latest commit date |
|---|---|---|
ec037fe8c0
commit 80f130bfad1dab93b95683fc39b87235682b8f72 upstream.
The documentation in rculist.h explains the absence of list_empty_rcu()
and cautions programmers against relying on a list_empty() ->
list_first() sequence in RCU safe code. This is because each of these
functions performs its own READ_ONCE() of the list head. This can lead
to a situation where the list_empty() sees a valid list entry, but the
subsequent list_first() sees a different view of list head state after a
modification.
In the case of dm-thin, this author had a production box crash from a GP
fault in the process_deferred_bios path. This function saw a valid list
head in get_first_thin() but when it subsequently dereferenced that and
turned it into a thin_c, it got the inside of the struct pool, since the
list was now empty and referring to itself. The kernel on which this
occurred printed both a warning about a refcount_t being saturated, and
a UBSAN error for an out-of-bounds cpuid access in the queued spinlock,
prior to the fault itself. When the resulting kdump was examined, it
was possible to see another thread patiently waiting in thin_dtr's
synchronize_rcu.
The thin_dtr call managed to pull the thin_c out of the active thins
list (and have it be the last entry in the active_thins list) at just
the wrong moment which lead to this crash.
Fortunately, the fix here is straight forward. Switch get_first_thin()
function to use list_first_or_null_rcu() which performs just a single
READ_ONCE() and returns NULL if the list is already empty.
This was run against the devicemapper test suite's thin-provisioning
suites for delete and suspend and no regressions were observed.
Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Fixes:
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||
| .. | ||
| bcache | ||
| persistent-data | ||
| dm-bio-prison-v1.c | ||
| dm-bio-prison-v1.h | ||
| dm-bio-prison-v2.c | ||
| dm-bio-prison-v2.h | ||
| dm-bio-record.h | ||
| dm-bufio.c | ||
| dm-builtin.c | ||
| dm-cache-background-tracker.c | ||
| dm-cache-background-tracker.h | ||
| dm-cache-block-types.h | ||
| dm-cache-metadata.c | ||
| dm-cache-metadata.h | ||
| dm-cache-policy-internal.h | ||
| dm-cache-policy-smq.c | ||
| dm-cache-policy.c | ||
| dm-cache-policy.h | ||
| dm-cache-target.c | ||
| dm-clone-metadata.c | ||
| dm-clone-metadata.h | ||
| dm-clone-target.c | ||
| dm-core.h | ||
| dm-crypt.c | ||
| dm-delay.c | ||
| dm-dust.c | ||
| dm-era-target.c | ||
| dm-exception-store.c | ||
| dm-exception-store.h | ||
| dm-flakey.c | ||
| dm-init.c | ||
| dm-integrity.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-writes.c | ||
| 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-rq.c | ||
| dm-rq.h | ||
| dm-service-time.c | ||
| dm-snap-persistent.c | ||
| dm-snap-transient.c | ||
| dm-snap.c | ||
| dm-stats.c | ||
| dm-stats.h | ||
| dm-stripe.c | ||
| dm-switch.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-unstripe.c | ||
| dm-verity-fec.c | ||
| dm-verity-fec.h | ||
| dm-verity-target.c | ||
| dm-verity-verify-sig.c | ||
| dm-verity-verify-sig.h | ||
| dm-verity.h | ||
| dm-writecache.c | ||
| dm-zero.c | ||
| dm-zoned-metadata.c | ||
| dm-zoned-reclaim.c | ||
| dm-zoned-target.c | ||
| dm-zoned.h | ||
| dm.c | ||
| dm.h | ||
| Kconfig | ||
| Makefile | ||
| md-bitmap.c | ||
| md-bitmap.h | ||
| md-cluster.c | ||
| md-cluster.h | ||
| md-faulty.c | ||
| md-linear.c | ||
| md-linear.h | ||
| md-multipath.c | ||
| md-multipath.h | ||
| md.c | ||
| md.h | ||
| raid0.c | ||
| raid0.h | ||
| raid1-10.c | ||
| raid1.c | ||
| raid1.h | ||
| raid5-cache.c | ||
| raid5-log.h | ||
| raid5-ppl.c | ||
| raid5.c | ||
| raid5.h | ||
| raid10.c | ||
| raid10.h | ||