linux.git/fs/btrfs/locking.c, branch v5.3

btrfs: Fix deadlock caused by missing memory barrier

2019-07-25T15:34:08+00:00

Commit 06297d8cefca ("btrfs: switch extent_buffer blocking_writers from
atomic to int") changed the type of blocking_writers but forgot to
adjust relevant code in btrfs_tree_unlock by converting the
smp_mb__after_atomic to smp_mb.  This opened up the possibility of a
deadlock due to re-ordering of setting blocking_writers and
checking/waking up the waiter. This particular lockup is explained in a
comment above waitqueue_active() function.

Fix it by converting the memory barrier to a full smp_mb, accounting
for the fact that blocking_writers is a simple integer.

Fixes: 06297d8cefca ("btrfs: switch extent_buffer blocking_writers from atomic to int")
Tested-by: Johannes Thumshirn 
Signed-off-by: Nikolay Borisov 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: switch extent_buffer write_locks from atomic to int

2019-07-02T10:30:47+00:00

The write_locks is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Reviewed-by: Nikolay Borisov 
Signed-off-by: David Sterba

btrfs: switch extent_buffer spinning_writers from atomic to int

2019-07-02T10:30:47+00:00

The spinning_writers is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Signed-off-by: David Sterba

btrfs: switch extent_buffer blocking_writers from atomic to int

2019-07-02T10:30:47+00:00

The blocking_writers is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Reviewed-by: Nikolay Borisov 
Signed-off-by: David Sterba

btrfs: trace: Introduce trace events for all btrfs tree locking events

2019-04-29T17:02:43+00:00

Unlike btrfs_tree_lock() and btrfs_tree_read_lock(), the remaining
functions in locking.c will not sleep, thus doesn't make much sense to
record their execution time.

Those events are introduced mainly for user space tool to audit and
detect lock leakage or dead lock.

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: trace: Introduce trace events for sleepable tree lock

2019-04-29T17:02:43+00:00

There are two tree lock events which can sleep:
- btrfs_tree_read_lock()
- btrfs_tree_lock()

Sometimes we may need to look into the concurrency picture of the fs.
For that case, we need the execution time of above two functions and the
owner of @eb.

Here we introduce a trace events for user space tools like bcc, to get
the execution time of above two functions, and get detailed owner info
where eBPF code can't.

All the overhead is hidden behind the trace events, so if events are not
enabled, there is no overhead.

These trace events also output bytenr and generation, allow them to be
pared with unlock events to pin down deadlock.

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: switch extent_buffer::lock_nested to bool

2019-04-29T17:02:21+00:00

The member is tracking simple status of the lock, we can use bool for
that and make some room for further space reduction in the structure.

Reviewed-by: Nikolay Borisov 
Reviewed-by: Johannes Thumshirn 
Signed-off-by: David Sterba

btrfs: use assertion helpers for extent buffer write lock counters

2019-04-29T17:02:21+00:00

Use the helpers where open coded. On non-debug builds, the warnings will
not trigger and extent_buffer::write_locks become unused and can be
moved to the appropriate section, saving a few bytes.

Reviewed-by: Nikolay Borisov 
Reviewed-by: Johannes Thumshirn 
Signed-off-by: David Sterba

btrfs: add assertion helpers for extent buffer write lock counters

2019-04-29T17:02:21+00:00

The write_locks are a simple counter to track locking balance and used
to assert tree locks.  Add helpers to make it conditionally work only in
DEBUG builds.  Will be used in followup patches.

Reviewed-by: Nikolay Borisov 
Reviewed-by: Johannes Thumshirn 
Signed-off-by: David Sterba

btrfs: use assertion helpers for extent buffer read lock counters

2019-04-29T17:02:21+00:00

Use the helpers where open coded. On non-debug builds, the warnings will
not trigger and extent_buffer::read_locks become unused and can be
moved to the appropriate section, saving a few bytes.

Reviewed-by: Nikolay Borisov 
Reviewed-by: Johannes Thumshirn 
Signed-off-by: David Sterba