Re: [PATCH] perf trace: always print return value for syscalls with set errpid

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Thu, Apr 03, 2025 at 08:26:52PM -0700, Howard Chu wrote:
> [Resend due to rejection by mailing list]
> 
> Hello Anubhav,
> 
> Thanks for doing this :)
> 
> On Thu, Apr 3, 2025 at 9:06 AM Anubhav Shelat <ashelat@redhat.com> wrote:
> >
> > Currently some syscalls that have errpid set to true do not print a
> > return value in perf trace. The syscalls that were consistently
> > observed were set_robust_list and rseq. This is because perf cannot find
> > their child process. This change ensures that the return value is always
> > printed.
> >
> > Before:
> >      0.256 ( 0.001 ms): set_robust_list(head: 0x7f09c77dba20, len: 24)                        =
> >      0.259 ( 0.001 ms): rseq(rseq: 0x7f09c77dc0e0, rseq_len: 32, sig: 1392848979)             =
> > After:
> >      0.270 ( 0.002 ms): set_robust_list(head: 0x7f0bb14a6a20, len: 24)                        = 0
> >      0.273 ( 0.002 ms): rseq(rseq: 0x7f0bb14a70e0, rseq_len: 32, sig: 1392848979)             = 0
> >
> > Signed-off-by: Anubhav Shelat <ashelat@redhat.com>
> 
> Reviewed-by: Howard Chu <howardchu95@gmail.com>

Thanks, applied after rewording it a bit to mention that this not
related to rseq/set_robust_list as those shouldn't be using errpid, but
that the problem predates that and added this, where the problem
started:

Fixes: 11c8e39f5133aed9 ("perf trace: Infrastructure to show COMM strings for syscalls returning PIDs")

- Arnaldo