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SubjectRe: [PATCH try #4] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline
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On May 26, 2015, at 5:24 PM, Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
>> On Tue, May 26, 2015 at 04:42:36PM -0400, Jarod Wilson wrote:
>>> On 5/8/2015 8:28 AM, Alexey Dobriyan wrote:
>>> /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with
>>>
>>> $ cat /proc/self/cmdline $(seq 1037) 2>/dev/null
>>>
>>> However, command line size was never limited to PAGE_SIZE but to 128 KB and
>>> relatively recently limitation was removed altogether.
>>>
>>> People noticed and ask questions:
>>> http://stackoverflow.com/questions/199130/how-do-i-increase-the-proc-pid-cmdline-4096-byte-limit
>>>
>>> seq file interface is not OK, because it kmalloc's for whole output and
>>> open + read(, 1) + sleep will pin arbitrary amounts of kernel memory.
>>> To not do that, limit must be imposed which is incompatible with
>>> arbitrary sized command lines.
>>>
>>> I apologize for hairy code, but this it direct consequence of command line
>>> layout in memory and hacks to support things like "init [3]".
>>>
>>> The loops are "unrolled" otherwise it is either macros which hide
>>> control flow or functions with 7-8 arguments with equal line count.
>>>
>>> There should be real setproctitle(2) or something.
>>>
>>> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
>>> Tested-by: Jarod Wilson <jarod@redhat.com>
>>> Acked-by: Jarod Wilson <jarod@redhat.com>
>>
>> Should have tested on more than just x86, it appears. We've started
>> hammering on this internally across all arches, and its exploded
>> multiple times on ppc64 now:
>>
>> [ 2717.074699] ------------[ cut here ]------------
>> [ 2717.074787] kernel BUG at fs/proc/base.c:244!
>
>> OE-------------- 3.10.0-255.el7.ppc64.debug #1
>
> Which BUG_ON is this?
>
> BUG_ON(*pos < 0);
> BUG_ON(arg_start > arg_end);
> BUG_ON(env_start > env_end);

Ah, sorry, right, might not be exactly the same with the back-up ported version... It was the env_start > env_end one.

--
Jarod Wilson

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