Re: [PATCH v2 1/3] Revert "perf session: Fix decompression of PERF_RECORD_COMPRESSED records"

Petr Malat
2020-11-30T11:41:17Z

Hi Jiří,
were you able to reproduce the issue? I may also upload perf-archive
if that would help.
Petr

On Tue, Nov 24, 2020 at 07:15:19PM +0100, Petr Malat wrote:
> Hi!
> On Tue, Nov 24, 2020 at 03:36:45PM +0100, Jiri Olsa wrote:
> > On Tue, Nov 24, 2020 at 11:29:15AM +0100, Petr Malat wrote:
> > > Both mmapped and compressed events can be split by the buffer boundary,
> > > it doesn't make sense to handle them differently.
> > I'm going to need more than this, if there's a problem
> > with current code please share more details, what's
> > broken and how it shows
> It's easy to trigger the problem - make a perf recording larger than
> MMAP_SIZE (32MB on 32-bit platform) and run perf report on it. There
> is a small chance recorded events will be aligned on the 32 MB
> boundary and in that case just repeat the test.
>
> The problem was introduced by "perf session: Avoid infinite loop when
> seeing invalid header.size", which instead of aborting the execution
> when there is a truncated event at the end of the file just terminated
> execution whenever there is a split event. Later then the problem has
> been noticed for compressed events and fixed by "perf session: Fix
> decompression of PERF_RECORD_COMPRESSED records" by effectively
> reverting "perf session: Avoid infinite loop when seeing invalid
> header.size" for compressed events, which left uncompressed events
> broken.
>
> I think the best is to revert these 2 changes and fix the original
> problem by aborting when there is no actual shift during remapping - as
> long as we shift, it's clear we must approach the end of the file so
> such an algorithm can't loop forever.
> BR,
> Petr