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From:   Helge Deller <deller@gmx.de>
To:     linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 0/3] Dump command line of faulting process to syslog
Date:   Mon,  1 Aug 2022 17:20:13 +0200
Message-Id: <20220801152016.36498-1-deller@gmx.de>
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This patch series allows the arch-specific kernel fault handlers to dump
in addition to the typical info (IP address, fault type, backtrace and so =
on)
the command line of the faulting process.

The motivation for this patch is that it's sometimes quite hard to find ou=
t and
annoying to not know which program *exactly* faulted when looking at the s=
yslog.

Some examples from the syslog are:

On parisc:
   do_page_fault() command=3D'cc1' type=3D15 address=3D0x00000000 in libc-=
2.33.so[f6abb000+184000]
   CPU: 1 PID: 13472 Comm: cc1 Tainted: G            E     5.10.133+ #45
   Hardware name: 9000/785/C8000

-> We see the "cc1" compiler crashed, but it would be useful to know which=
 file was compiled.

With this patch series, the kernel now prints in addition:
   cc1[13472] cmdline: /usr/lib/gcc/hppa-linux-gnu/12/cc1 -quiet @/tmp/ccR=
kFSfY -imultilib . -imultiarch hppa-linux-gnu -D USE_MINIINTERPRETER -D NO=
_REGS -D _HPUX_SOURCE -D NOSMP -D THREADED_RTS -include /build/ghc/ghc-9.0=
.2/includes/dist-install/build/ghcversion.h -iquote compiler/GHC/Iface -qu=
iet -dumpdir /tmp/ghc13413_0/ -dumpbase ghc_5.hc -dumpbase-ext .hc -O -Wim=
plicit -fno-PIC -fwrapv -fno-builtin -fno-strict-aliasing -o /tmp/ghc13413=
_0/ghc_5.s

-> now we know that cc1 crashed while compiling some haskell code.

Another parisc example:
   do_page_fault() command=3D'ld.so.1' type=3D15 address=3D0x565921d8 in l=
ibc.so[f7339000+1bb000]
   CPU: 1 PID: 1151 Comm: cc1 Tainted: G            E     5.10.133+ #45
   Hardware name: 9000/785/C8000

-> apparently here a program from the glibc testsuite segfaulted.

With this patch we now additionally get:
   ld.so.1[1151] cmdline: /home/gnu/glibc/objdir/elf/ld.so.1 --library-pat=
h /home/gnu/glibc/objdir:/home/gnu/glibc/objdir/math:/home/gnu/
        /home/gnu/glibc/objdir/malloc/tst-safe-linking-malloc-hugetlb1

-> it was the tst-safe-linking-malloc-hugetlb1 testcase which faulted.

An example of a typical x86 fault shows up as:
   crash[2326]: segfault at 0 ip 0000561a7969c12e sp 00007ffe97a05630 erro=
r 6 in crash[561a7969c000+1000]
   Code: 68 ff ff ff c6 05 19 2f 00 00 01 5d c3 0f 1f 80 00 00 00 00 c3 0f=
 1f 80 00 00 00 00 e9 7b ff ff ff 55 48 89 e5 b8 00 00 00 00 <c7> 00 01 00=
 00 00 b8 00 00 00 00 5d c3 0f 1f 44 00 00 41 57 4c 8d

-> with this patch we now will see the whole command line:
   crash[2326] cmdline: ./crash test_write_to_page_0

The patches are relatively small, and reuses functions which are used
to create the output for the /proc/<pid>/cmdline files.

This is the version 1 of the patch series.
I'm interested if people find this useful too, and if so, I'm
happy for any feedback on those patches.

Thanks!
Helge

Helge Deller (3):
  proc: Add get_task_cmdline_kernel() function
  lib/dump_stack: Add dump_stack_print_cmdline() and wire up in
    dump_stack_print_info()
  x86/fault: Dump command line of faulting process to syslog

 arch/x86/mm/fault.c     |  2 ++
 fs/proc/base.c          | 68 +++++++++++++++++++++++++++--------------
 include/linux/printk.h  |  5 +++
 include/linux/proc_fs.h |  5 +++
 lib/dump_stack.c        | 17 +++++++++++
 5 files changed, 74 insertions(+), 23 deletions(-)

=2D-
2.37.1