Hi Steven, Steven Rostedt <rost...@goodmis.org> writes:
> On Mon, 05 Feb 2024 14:16:30 +0100 > Sven Schnelle <sv...@linux.ibm.com> wrote: >> >> Another issue i'm hitting sometimes is this part: >> >> csum1=`md5sum trace` >> sleep $SLEEP_TIME >> csum2=`md5sum trace` >> >> if [ "$csum1" != "$csum2" ]; then >> fail "Tracing file is still changing" >> fi >> >> This is because the command line was replaced in the >> saved_cmdlines_buffer, an example diff between both files >> is: > > [..] > >> >> This can be improved by: >> >> echo 32768 > /sys/kernel/tracing/saved_cmdlines_size >> >> But this is of course not a fix - should we maybe replace the program >> name with <...> before comparing, remove the check completely, or do >> anything else? What do you think? > > Hmm, actually I would say that this exposes a real bug. Not a major > one, but one that I find annoying. The saved commandlines should only > be updated when a trace event occurs. But really, it should only be > updated if one is added to the ring buffer. If the ring buffer isn't > being updated, we shouldn't be adding new command lines. > > There may be a location that has tracing off but still updating the > cmdlines which will break the saved cache. Ok, my understanding is that it will override the entry in the list if another process comes up with the same PID. But i haven't read the code carefully - let me do that now.
