Messages in this thread | | | Date | Fri, 7 Nov 2008 20:51:57 +0300 | From | Alexey Dobriyan <> | Subject | Re: [patch] add /proc/pid/stack to dump task's stack trace |
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On Fri, Nov 07, 2008 at 10:29:02AM +0100, Ingo Molnar wrote: > > * Andrew Morton <akpm@linux-foundation.org> wrote: > > > On Fri, 7 Nov 2008 10:03:04 +0100 Ingo Molnar <mingo@elte.hu> wrote: > > > > > task running on this CPU: > > > > > > # cat /proc/self/stack > > > [<ffffffff80216f79>] save_stack_trace_tsk+0x26/0x44 > > > [<ffffffff802f59a5>] proc_pid_stack+0x6e/0xd3 > > > [<ffffffff802f6da3>] proc_info_read+0x68/0xba > > > [<ffffffff802b2f17>] vfs_read+0xa9/0xe3 > > > [<ffffffff802b301f>] sys_read+0x4c/0x73 > > > [<ffffffff8020c23b>] system_call_fastpath+0x16/0x1b > > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > So we provide a means by which process A can sample process B's > > instruction pointer? Even if it's in random.c or crypto code? > > There's a little project for someone. > > yes - like "echo p > /proc/sysrq-trigger" and sysrq-t. Although unlike > sysrq-p, the IP itself isnt printed, just the stack trace - but > there's indeed a correlation. > > > I guess the 0400 mode on that file will suffice... > > correct, 0400 is used already in the present patch: > > phoenix:~> cat /proc/1/stack > cat: /proc/1/stack: Permission denied > > but that is _not_ enough, it should be narrowed even more, to the > boundaries that i pointed out in my first review feedback mail, and > which is not implemented yet: > > 1) only root should be allowed to do this - i.e. file needs to be > root-owned. > > 2) there also needs to be a .config entry for folks to be able to > turn it off altogether - just like folks can turn off sysrq-t > dumping via the .config.
In the name of everything holy, don't add another config option. It's a _tiny_ piece of code and you have select STACKTRACE via fault injection, latencytop or lockdep before that.
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