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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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