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    SubjectRe: mmotm 2010-04-05 - another RCU whinge (not network this time)
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    On Fri, 09 Apr 2010 16:16:14 PDT, "Paul E. McKenney" said:
    > On Thu, Apr 08, 2010 at 07:57:28PM -0400, Valdis.Kletnieks@vt.edu wrote:
    > > On Mon, 05 Apr 2010 16:09:45 PDT, akpm@linux-foundation.org said:
    > > > The mm-of-the-moment snapshot 2010-04-05-16-09 has been uploaded to
    > > >
    > > > http://userweb.kernel.org/~akpm/mmotm/
    > >
    > > Hit another one. I seem to be on a roll...
    > >
    > > Seen in dmesg, happened near end of the initrd..
    > >
    > > [ 26.756864]
    > > [ 26.756866] ===================================================
    > > [ 26.756869] [ INFO: suspicious rcu_dereference_check() usage. ]
    > > [ 26.756871] ---------------------------------------------------
    > > [ 26.756874] fs/proc/array.c:241 invoked rcu_dereference_check() without protection!
    >
    > Color me confused. I cloned James Toy's git repository at
    > git://zen-kernel.org/kernel/mmotm.git, and gitk claims that I am on tag
    > 2010-04-05-16-09, which matches the string above. But when I look at
    > fs/proc/array.c near line 241, I see:

    Andrew's -mm tree has 3 patches from Oleg Nesterov that hit that file, so the
    code is different from what you show. Color *me* confused why your clone of
    mmotm.git doesn't seem to contain them - I'm not sure how James Toy builds
    that git tree. Perhaps the tag is applied before those patches are - the
    'mm.patch' that updates the Makefile with the version is usually in the
    *middle* of the 'series' file. What does HEAD of that tree look like?

    My tree has:

    /* needs ->siglock or rcu_read_lock() */
    static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
    sigset_t *catch)
    {
    struct sighand_struct *sighand = rcu_dereference(p->sighand);

    And that rcu_dereference() does it.

    Oleg, looks like proc-make-collect_sigign_sigcatch-rcu-safe.patch is the
    offender here, it added the line that causes the whinge.


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