- Limit time interrupts are disabled in rb_check_pages()
The rb_check_pages() is called after the ring buffer size is updated to
make sure that the ring buffer has not been corrupted. Commit
c2274b908d ("ring-buffer: Fix a race between readers and resize
checks") fixed a race with the check pages and simultaneous resizes to the
ring buffer by adding a raw_spin_lock_irqsave() around the check
operation. Although this was a simple fix, it would hold interrupts
disabled for non determinative amount of time. This could harm PREEMPT_RT
operations.
Instead, modify the logic by adding a counter when the buffer is modified
and to release the raw_spin_lock() at each iteration. It checks the
counter under the lock to see if a modification happened during the loop,
and if it did, it would restart the loop up to 3 times. After 3 times, it
will simply exit the check, as it is unlikely that would ever happen as
buffer resizes are rare occurrences.
- Replace some open coded str_low_high() with the helper
- Fix some documentation/comments
-----BEGIN PGP SIGNATURE-----
iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCZz5KNxQccm9zdGVkdEBn
b29kbWlzLm9yZwAKCRAp5XQQmuv6qiANAP4/6cSGOhQgIkaN8UsKmWTfBqU89JK2
a4tqAZWKsQormgEAkDLPD0Lda0drmu/Dwnr/klS21yyLcQBzyX1CYw9G4gY=
=jkLz
-----END PGP SIGNATURE-----
Merge tag 'trace-ring-buffer-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull trace ring-buffer updates from Steven Rostedt:
- Limit time interrupts are disabled in rb_check_pages()
rb_check_pages() is called after the ring buffer size is updated to
make sure that the ring buffer has not been corrupted. Commit
c2274b908d ("ring-buffer: Fix a race between readers and resize
checks") fixed a race with the check pages and simultaneous resizes
to the ring buffer by adding a raw_spin_lock_irqsave() around the
check operation. Although this was a simple fix, it would hold
interrupts disabled for non determinative amount of time. This could
harm PREEMPT_RT operations.
Instead, modify the logic by adding a counter when the buffer is
modified and to release the raw_spin_lock() at each iteration. It
checks the counter under the lock to see if a modification happened
during the loop, and if it did, it would restart the loop up to 3
times. After 3 times, it will simply exit the check, as it is
unlikely that would ever happen as buffer resizes are rare
occurrences.
- Replace some open coded str_low_high() with the helper
- Fix some documentation/comments
* tag 'trace-ring-buffer-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ring-buffer: Correct a grammatical error in a comment
ring-buffer: Use str_low_high() helper in ring_buffer_producer()
ring-buffer: Reorganize kerneldoc parameter names
ring-buffer: Limit time with disabled interrupts in rb_check_pages()
f1db825805