* Peter Zijlstra <[email protected]> wrote:
> In perf_output_put_handle(), an IRQ/NMI can happen in below location and > write records to the same ring buffer: > ... > local_dec_and_test(&rb->nest) > ... <-- an IRQ/NMI can happen here > rb->user_page->data_head = head; > ... > > In this case, a value A is written to data_head in the IRQ, then a value > B is written to data_head after the IRQ. And A > B. As a result, > data_head is temporarily decreased from A to B. And a reader may see > data_head < data_tail if it read the buffer frequently enough, which > creates unexpected behaviors. > > This can be fixed by moving dec(&rb->nest) to after updating data_head, > which prevents the IRQ/NMI above from updating data_head. > > Cc: Arnaldo Carvalho de Melo <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Jiri Olsa <[email protected]> > Cc: Namhyung Kim <[email protected]> > Cc: Alexander Shishkin <[email protected]> > Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing > IRQ-disables") > Signed-off-by: Yabin Cui <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Link: https://lkml.kernel.org/r/[email protected] So these are missing a bunch of: From: Yabin Cui <[email protected]> lines, right? Thanks, Ingo
