[Crash-utility] Crash-utility Digest, Vol 179, Issue 4

[David Wysochanski]

Hi Lianbo

On Sat, Aug 8, 2020 at 10:46 PM lijiang <lijiang at redhat.com> wrote:
>
> 在 2020年08月07日 00:00, crash-utility-request at redhat.com 写道:
> > Message: 5
> > Date: Thu,  6 Aug 2020 09:30:22 -0400
> > From: Dave Wysochanski <dwysocha at redhat.com>
> > To: crash-utility at redhat.com
> > Subject: [Crash-utility] [PATCH v3] Fix "log" command when crash is
> >       started with "--minimal" option
> > Message-ID: <20200806133022.2127538-1-dwysocha at redhat.com>
> >
> > Commit c86250bce29f introduced the useful '-T' option to print the
> > log timestamp in human-readable form.  However, this option does
> > not work when crash is invoked with '--minimal' mode, and if tried,
> > crash will spin at 100% and continuously crash at a divide by 0
> > because machdep->hz == 0.
> >
> > Fix this by disallowing this option in minimal mode.  In addition,
> > only calculate the logic to calculate kt->boot_date.tv_sec
> > when this option is enabled.
> >
> Hi, Dave Wysochanski
>
> Thank you for the patch.
>
> > Fixes: c86250bce29f ("Introduction of the "log -T" option...")
> > Signed-off-by: Dave Wysochanski <dwysocha at redhat.com>
> > Reviewed-by: Wang Long <w at laoqinren.net>
> > Tested-by: Mathias Krause <minipli at grsecurity.net>
> > ---
> >  kernel.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel.c b/kernel.c
> > index 5ed6021..95119f3 100644
> > --- a/kernel.c
> > +++ b/kernel.c
> > @@ -4939,7 +4939,10 @@ cmd_log(void)
> >          if (argerrs)
> >                  cmd_usage(pc->curcmd, SYNOPSIS);
> >
> > -     if (kt->boot_date.tv_sec == 0) {
> > +     if (msg_flags & SHOW_LOG_CTIME && pc->flags & MINIMAL_MODE)
> > +             error(FATAL, "log: option 'T' not available in minimal mode\n");
> > +
> > +     if (msg_flags & SHOW_LOG_CTIME && kt->boot_date.tv_sec == 0) {
>
> The above two 'if' statements have the same checking condition, would you mind putting them together
> as a statement block? E.g:
>
Sure I can resubmit a fixup of v4 patch once there are no more changes needed.

> +       if (msg_flags & SHOW_LOG_CTIME) {
> +               if (pc->flags & MINIMAL_MODE) {
> +                       error(WARNING, "the option '-T' not available in minimal mode\n");
> +                       return;
> +               }
> +
> +               if (kt->boot_date.tv_sec == 0) {
> ...
> +               }
>         }
>
> In addition, might it be more reasonable to issue a warning instead of a fatal error?
>

If you use WARNING it will not fix the infinite loop / CPU spin at
100%.  You have to CTRL-C the crash program to get the prompt back.
So I do not think this is a good idea.

This is easily reproducible on any vmcore you can see for yourself if
you want.   But here is the backtrace in GDB:

crash> log -T
[Detaching after fork from child process 2669642]
log: WARNING: log: option 'T' not available in minimal mode

Program received signal SIGFPE, Arithmetic exception.
0x00000000004e5ecf in cmd_log () at kernel.c:4950
4950                    kt->boot_date.tv_sec = kt->date.tv_sec - uptime_sec;
Missing separate debuginfos, use: yum debuginfo-install
zlib-1.2.11-13.el8.x86_64
(gdb) bt
#0  0x00000000004e5ecf in cmd_log () at kernel.c:4950
#1  0x0000000000463ea9 in exec_command () at main.c:880
#2  0x00000000004640da in main_loop () at main.c:827
#3  0x00000000006c0ce3 in captured_command_loop (data=<optimized out>)
at main.c:258
#4  0x00000000006bf5ce in catch_errors (func=0x6c0cd0
<captured_command_loop>, func_args=0x0, errstring=0x91b926 "", mask=6)
at exceptions.c:557
#5  0x00000000006c1bb6 in captured_main (data=<optimized out>) at main.c:1064
#6  0x00000000006bf5ce in catch_errors (func=0x6c0df0 <captured_main>,
func_args=0x7fffffffe260, errstring=0x91b926 "", mask=6) at
exceptions.c:557
#7  0x00000000006c0ae4 in gdb_main (args=<optimized out>) at main.c:1079
#8  0x00000000006c0b1e in gdb_main_entry (argc=<optimized out>,
argv=<optimized out>, argv at entry=0x7fffffffe3c8) at main.c:1099
#9  0x00000000004f86d4 in gdb_main_loop (argc=<optimized out>,
argc at entry=4, argv=argv at entry=0x7fffffffe3c8) at gdb_interface.c:76
#10 0x0000000000462707 in main (argc=4, argv=0x7fffffffe3c8) at main.c:708
(gdb) c
Continuing.

Program received signal SIGFPE, Arithmetic exception.
0x00000000004e5ecf in cmd_log () at kernel.c:4950
4950                    kt->boot_date.tv_sec = kt->date.tv_sec - uptime_sec;
(gdb) bt
#0  0x00000000004e5ecf in cmd_log () at kernel.c:4950
#1  0x0000000000463ea9 in exec_command () at main.c:880
#2  0x00000000004640da in main_loop () at main.c:827
#3  0x00000000006c0ce3 in captured_command_loop (data=<optimized out>)
at main.c:258
#4  0x00000000006bf5ce in catch_errors (func=0x6c0cd0
<captured_command_loop>, func_args=0x0, errstring=0x91b926 "", mask=6)
at exceptions.c:557
#5  0x00000000006c1bb6 in captured_main (data=<optimized out>) at main.c:1064
#6  0x00000000006bf5ce in catch_errors (func=0x6c0df0 <captured_main>,
func_args=0x7fffffffe260, errstring=0x91b926 "", mask=6) at
exceptions.c:557
#7  0x00000000006c0ae4 in gdb_main (args=<optimized out>) at main.c:1079
#8  0x00000000006c0b1e in gdb_main_entry (argc=<optimized out>,
argv=<optimized out>, argv at entry=0x7fffffffe3c8) at main.c:1099
#9  0x00000000004f86d4 in gdb_main_loop (argc=<optimized out>,
argc at entry=4, argv=argv at entry=0x7fffffffe3c8) at gdb_interface.c:76
#10 0x0000000000462707 in main (argc=4, argv=0x7fffffffe3c8) at main.c:708
(gdb) quit
A debugging session is active.

        Inferior 1 [process 2669636] will be killed.

Quit anyway? (y or n) y