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3d3a2e610e
linux/fs/btrfs
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David Sterba 3d3a2e610e btrfs: add barriers to btrfs_sync_log before log_commit_wait wakeups 
Currently the code assumes that there's an implied barrier by the
sequence of code preceding the wakeup, namely the mutex unlock.

As Nikolay pointed out:

I think this is wrong (not your code) but the original assumption that
the RELEASE semantics provided by mutex_unlock is sufficient.
According to memory-barriers.txt:

Section 'LOCK ACQUISITION FUNCTIONS' states:

 (2) RELEASE operation implication:

     Memory operations issued before the RELEASE will be completed before the
     RELEASE operation has completed.

     Memory operations issued after the RELEASE *may* be completed before the
     RELEASE operation has completed.

(I've bolded the may portion)

The example given there:

As an example, consider the following:

    *A = a;
    *B = b;
    ACQUIRE
    *C = c;
    *D = d;
    RELEASE
    *E = e;
    *F = f;

The following sequence of events is acceptable:

    ACQUIRE, {*F,*A}, *E, {*C,*D}, *B, RELEASE

So if we assume that *C is modifying the flag which the waitqueue is checking,
and *E is the actual wakeup, then those accesses can be re-ordered...

IMHO this code should be considered broken...
---

To be on the safe side, add the barriers. The synchronization logic
around log using the mutexes and several other threads does not make it
easy to reason for/against the barrier.

CC: Nikolay Borisov <nborisov@suse.com>
Link: https://lkml.kernel.org/r/6ee068d8-1a69-3728-00d1-d86293d43c9f@suse.com
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-28 18:23:06 +02:00
..
tests btrfs: Remove fs_info argument from __remove_from_free_space_tree 2018-05-28 18:07:35 +02:00
acl.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
async-thread.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
async-thread.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
backref.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
backref.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
btrfs_inode.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
check-integrity.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
check-integrity.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
compression.c for-4.17-part2-tag 2018-04-15 18:08:35 -07:00
compression.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
ctree.c btrfs: fix reading stale metadata blocks after degraded raid1 mounts 2018-05-17 14:18:25 +02:00
ctree.h btrfs: introduce conditional wakeup helpers 2018-05-28 18:23:04 +02:00
dedupe.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
delayed-inode.c btrfs: delayed-inode: Remove wrong qgroup meta reservation calls 2018-04-18 16:46:55 +02:00
delayed-inode.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
delayed-ref.c btrfs: split delayed ref head initialization and addition 2018-05-28 18:07:32 +02:00
delayed-ref.h btrfs: Drop fs_info parameter from btrfs_merge_delayed_refs 2018-05-28 18:07:20 +02:00
dev-replace.c btrfs: Remove delayed_iput parameter of btrfs_start_delalloc_roots 2018-05-28 18:07:28 +02:00
dev-replace.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
dir-item.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
disk-io.c btrfs: Do super block verification before writing it to disk 2018-05-28 18:07:36 +02:00
disk-io.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
export.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
export.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
extent_io.c btrfs: Remove tree argument from extent_writepages 2018-05-28 18:07:20 +02:00
extent_io.h btrfs: Remove tree argument from extent_writepages 2018-05-28 18:07:20 +02:00
extent_map.c btrfs: use fs_info for btrfs_handle_em_exist tracepoint 2018-05-28 18:07:17 +02:00
extent_map.h btrfs: use fs_info for btrfs_handle_em_exist tracepoint 2018-05-28 18:07:17 +02:00
extent-tree.c btrfs: Remove fs_info argument from add_to_free_space_tree 2018-05-28 18:07:36 +02:00
file-item.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
file.c btrfs: Fix wrong btrfs_delalloc_release_extents parameter 2018-04-18 16:46:57 +02:00
free-space-cache.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
free-space-cache.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
free-space-tree.c btrfs: Remove fs_info argument from populate_free_space_tree 2018-05-28 18:07:36 +02:00
free-space-tree.h btrfs: Remove fs_info argument from add_to_free_space_tree 2018-05-28 18:07:36 +02:00
inode-item.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
inode-map.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
inode-map.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
inode.c btrfs: take the last remnants of ->d_fsdata use out 2018-05-28 18:07:37 +02:00
ioctl.c btrfs: remove redundant btrfs_balance_control::fs_info 2018-05-28 18:07:30 +02:00
Kconfig btrfs: add SPDX header to Kconfig 2018-04-12 16:29:55 +02:00
locking.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
locking.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
lzo.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
Makefile btrfs: Remove custom crc32c init code 2018-03-26 15:09:39 +02:00
math.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
ordered-data.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ordered-data.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
orphan.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
print-tree.c btrfs: print-tree: Add eb locking status output for debug build 2018-05-28 18:07:26 +02:00
print-tree.h btrfs: print-tree: debugging output enhancement 2018-04-20 19:18:16 +02:00
props.c btrfs: property: Set incompat flag if lzo/zstd compression is set 2018-05-17 14:18:25 +02:00
props.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
qgroup.c btrfs: qgroup: Finish rescan when hit the last leaf of extent tree 2018-05-28 18:23:03 +02:00
qgroup.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
raid56.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
raid56.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
rcu-string.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
reada.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ref-verify.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ref-verify.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
relocation.c btrfs: remove unused fs_info parameter 2018-05-28 18:07:27 +02:00
root-tree.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
scrub.c btrfs: trace: Add trace points for unused block groups 2018-05-28 18:07:28 +02:00
send.c btrfs: incremental send, improve rmdir performance for large directory 2018-05-28 18:07:32 +02:00
send.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
struct-funcs.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
super.c btrfs: return original error code when failing from option parsing 2018-05-28 18:07:30 +02:00
sysfs.c btrfs: rename struct btrfs_fs_devices::list 2018-05-28 18:07:21 +02:00
sysfs.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
transaction.c btrfs: qgroup: Commit transaction in advance to reduce early EDQUOT 2018-04-18 16:46:47 +02:00
transaction.h btrfs: qgroup: Commit transaction in advance to reduce early EDQUOT 2018-04-18 16:46:47 +02:00
tree-checker.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
tree-checker.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
tree-defrag.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
tree-log.c btrfs: add barriers to btrfs_sync_log before log_commit_wait wakeups 2018-05-28 18:23:06 +02:00
tree-log.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
ulist.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ulist.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
uuid-tree.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
volumes.c btrfs: remove redundant btrfs_balance_control::fs_info 2018-05-28 18:07:30 +02:00
volumes.h btrfs: remove redundant btrfs_balance_control::fs_info 2018-05-28 18:07:30 +02:00
xattr.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
xattr.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
zlib.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
zstd.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00