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Message-ID: <aCdwycWxRnbbHUke@google.com>
Date: Fri, 16 May 2025 10:07:21 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Sergei Trofimovich <slyich@...il.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
"Liang, Kan" <kan.liang@...ux.intel.com>,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf unwind-libdw: skip non-regular files
Hello,
On Mon, May 05, 2025 at 06:44:19PM +0100, Sergei Trofimovich wrote:
> Without the change `perf `hangs up on charaster devices. On my system
> it's enough to run system-wide sampler for a few seconds to get the
> hangup:
>
> $ perf record -a -g --call-graph=dwarf
> $ perf report
> # hung
>
> `strace` shows that hangup happens on reading on a character device
> `/dev/dri/renderD128`
>
> $ strace -y -f -p 2780484
> strace: Process 2780484 attached
> pread64(101</dev/dri/renderD128>, strace: Process 2780484 detached
>
> It's call trace descends into `elfutils`:
>
> $ gdb -p 2780484
> (gdb) bt
> #0 0x00007f5e508f04b7 in __libc_pread64 (fd=101, buf=0x7fff9df7edb0, count=0, offset=0)
> at ../sysdeps/unix/sysv/linux/pread64.c:25
> #1 0x00007f5e52b79515 in read_file () from /<<NIX>>/elfutils-0.192/lib/libelf.so.1
> #2 0x00007f5e52b25666 in libdw_open_elf () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #3 0x00007f5e52b25907 in __libdw_open_file () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #4 0x00007f5e52b120a9 in dwfl_report_elf@@ELFUTILS_0.156 ()
> from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #5 0x000000000068bf20 in __report_module (al=al@...ry=0x7fff9df80010, ip=ip@...ry=139803237033216, ui=ui@...ry=0x5369b5e0)
> at util/dso.h:537
> #6 0x000000000068c3d1 in report_module (ip=139803237033216, ui=0x5369b5e0) at util/unwind-libdw.c:114
> #7 frame_callback (state=0x535aef10, arg=0x5369b5e0) at util/unwind-libdw.c:242
> #8 0x00007f5e52b261d3 in dwfl_thread_getframes () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #9 0x00007f5e52b25bdb in get_one_thread_cb () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #10 0x00007f5e52b25faa in dwfl_getthreads () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #11 0x00007f5e52b26514 in dwfl_getthread_frames () from /<<NIX>>/elfutils-0.192/lib/libdw.so.1
> #12 0x000000000068c6ce in unwind__get_entries (cb=cb@...ry=0x5d4620 <unwind_entry>, arg=arg@...ry=0x10cd5fa0,
> thread=thread@...ry=0x1076a290, data=data@...ry=0x7fff9df80540, max_stack=max_stack@...ry=127,
> best_effort=best_effort@...ry=false) at util/thread.h:152
> #13 0x00000000005dae95 in thread__resolve_callchain_unwind (evsel=0x106006d0, thread=0x1076a290, cursor=0x10cd5fa0,
> sample=0x7fff9df80540, max_stack=127, symbols=true) at util/machine.c:2939
> #14 thread__resolve_callchain_unwind (thread=0x1076a290, cursor=0x10cd5fa0, evsel=0x106006d0, sample=0x7fff9df80540,
> max_stack=127, symbols=true) at util/machine.c:2920
> #15 __thread__resolve_callchain (thread=0x1076a290, cursor=0x10cd5fa0, evsel=0x106006d0, evsel@...ry=0x7fff9df80440,
> sample=0x7fff9df80540, parent=parent@...ry=0x7fff9df804a0, root_al=root_al@...ry=0x7fff9df80440, max_stack=127, symbols=true)
> at util/machine.c:2970
> #16 0x00000000005d0cb2 in thread__resolve_callchain (thread=<optimized out>, cursor=<optimized out>, evsel=0x7fff9df80440,
> sample=<optimized out>, parent=0x7fff9df804a0, root_al=0x7fff9df80440, max_stack=127) at util/machine.h:198
> #17 sample__resolve_callchain (sample=<optimized out>, cursor=<optimized out>, parent=parent@...ry=0x7fff9df804a0,
> evsel=evsel@...ry=0x106006d0, al=al@...ry=0x7fff9df80440, max_stack=max_stack@...ry=127) at util/callchain.c:1127
> #18 0x0000000000617e08 in hist_entry_iter__add (iter=iter@...ry=0x7fff9df80480, al=al@...ry=0x7fff9df80440, max_stack_depth=127,
> arg=arg@...ry=0x7fff9df81ae0) at util/hist.c:1255
> #19 0x000000000045d2d0 in process_sample_event (tool=0x7fff9df81ae0, event=<optimized out>, sample=0x7fff9df80540,
> evsel=0x106006d0, machine=<optimized out>) at builtin-report.c:334
> #20 0x00000000005e3bb1 in perf_session__deliver_event (session=0x105ff2c0, event=0x7f5c7d735ca0, tool=0x7fff9df81ae0,
> file_offset=2914716832, file_path=0x105ffbf0 "perf.data") at util/session.c:1367
> #21 0x00000000005e8d93 in do_flush (oe=0x105ffa50, show_progress=false) at util/ordered-events.c:245
> #22 __ordered_events__flush (oe=0x105ffa50, how=OE_FLUSH__ROUND, timestamp=<optimized out>) at util/ordered-events.c:324
> #23 0x00000000005e1f64 in perf_session__process_user_event (session=0x105ff2c0, event=0x7f5c7d752b18, file_offset=2914835224,
> file_path=0x105ffbf0 "perf.data") at util/session.c:1419
> #24 0x00000000005e47c7 in reader__read_event (rd=rd@...ry=0x7fff9df81260, session=session@...ry=0x105ff2c0,
> --Type <RET> for more, q to quit, c to continue without paging--
> quit
> prog=prog@...ry=0x7fff9df81220) at util/session.c:2132
> #25 0x00000000005e4b37 in reader__process_events (rd=0x7fff9df81260, session=0x105ff2c0, prog=0x7fff9df81220)
> at util/session.c:2181
> #26 __perf_session__process_events (session=0x105ff2c0) at util/session.c:2226
> #27 perf_session__process_events (session=session@...ry=0x105ff2c0) at util/session.c:2390
> #28 0x0000000000460add in __cmd_report (rep=0x7fff9df81ae0) at builtin-report.c:1076
> #29 cmd_report (argc=<optimized out>, argv=<optimized out>) at builtin-report.c:1827
> #30 0x00000000004c5a40 in run_builtin (p=p@...ry=0xd8f7f8 <commands+312>, argc=argc@...ry=1, argv=argv@...ry=0x7fff9df844b0)
> at perf.c:351
> #31 0x00000000004c5d63 in handle_internal_command (argc=argc@...ry=1, argv=argv@...ry=0x7fff9df844b0) at perf.c:404
> #32 0x0000000000442de3 in run_argv (argcp=<synthetic pointer>, argv=<synthetic pointer>) at perf.c:448
> #33 main (argc=<optimized out>, argv=0x7fff9df844b0) at perf.c:556
>
> The hangup happens because nothing in` perf` or `elfutils` checks if a
> mapped file is easily readable.
>
> The change conservatively skips all non-regular files.
>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Arnaldo Carvalho de Melo <acme@...nel.org>
> CC: Namhyung Kim <namhyung@...nel.org>
> CC: Mark Rutland <mark.rutland@....com>
> CC: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> CC: Jiri Olsa <jolsa@...nel.org>
> CC: Ian Rogers <irogers@...gle.com>
> CC: Adrian Hunter <adrian.hunter@...el.com>
> CC: "Liang, Kan" <kan.liang@...ux.intel.com>
> CC: linux-perf-users@...r.kernel.org
> Signed-off-by: Sergei Trofimovich <slyich@...il.com>
Acked-by: Namhyung Kim <namhyung@...nel.org>
Thanks,
Namhyung
> ---
> tools/perf/util/unwind-libdw.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> index 793d11832694..ae70fb56a057 100644
> --- a/tools/perf/util/unwind-libdw.c
> +++ b/tools/perf/util/unwind-libdw.c
> @@ -84,8 +84,11 @@ static int __report_module(struct addr_location *al, u64 ip,
> char filename[PATH_MAX];
>
> __symbol__join_symfs(filename, sizeof(filename), dso__long_name(dso));
> - mod = dwfl_report_elf(ui->dwfl, dso__short_name(dso), filename, -1,
> - base, false);
> + /* Don't hang up on device files like /dev/dri/renderD128. */
> + if (is_regular_file(filename)) {
> + mod = dwfl_report_elf(ui->dwfl, dso__short_name(dso), filename, -1,
> + base, false);
> + }
> }
> if (!mod) {
> char filename[PATH_MAX];
> --
> 2.49.0
>
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