On Wed, 3 Jul 2024 09:53:14 +0200 Petr Pavlu <petr.pa...@suse.com> wrote:
> The function rb_check_pages() validates the integrity of a specified > per-CPU tracing ring buffer. It does so by traversing the underlying > linked list and checking its next and prev links. > > To guarantee that the list isn't modified during the check, a caller > typically needs to take cpu_buffer->reader_lock. This prevents the check > from running concurrently, for example, with a potential reader which > can make the list temporarily inconsistent when swapping its old reader > page into the buffer. > > A problem with this approach is that the time when interrupts are > disabled is non-deterministic, dependent on the ring buffer size. This > particularly affects PREEMPT_RT because the reader_lock is a raw > spinlock which doesn't become sleepable on PREEMPT_RT kernels. > > Modify the check so it still attempts to traverse the entire list, but > gives up the reader_lock between checking individual pages. Introduce > for this purpose a new variable ring_buffer_per_cpu.pages_era which is I'm dumb. What's an "era"? -- Steve > bumped any time the list is modified. The value is used by > rb_check_pages() to detect such a change and restart the check. > > Signed-off-by: Petr Pavlu <petr.pa...@suse.com>
