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    Subject[PATCH 3.8 057/116] mm/memory-failure.c-failure: send right signal code to correct thread
    Date
    3.8.13.27 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tony Luck <tony.luck@intel.com>

    commit a70ffcac741d31a406c1d2b832ae43d658e7e1cf upstream.

    When a thread in a multi-threaded application hits a machine check because
    of an uncorrectable error in memory - we want to send the SIGBUS with
    si.si_code = BUS_MCEERR_AR to that thread. Currently we fail to do that
    if the active thread is not the primary thread in the process.
    collect_procs() just finds primary threads and this test:

    if ((flags & MF_ACTION_REQUIRED) && t == current) {

    will see that the thread we found isn't the current thread and so send a
    si.si_code = BUS_MCEERR_AO to the primary (and nothing to the active
    thread at this time).

    We can fix this by checking whether "current" shares the same mm with the
    process that collect_procs() said owned the page. If so, we send the
    SIGBUS to current (with code BUS_MCEERR_AR).

    Signed-off-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Reported-by: Otto Bruggeman <otto.g.bruggeman@intel.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Chen Gong <gong.chen@linux.jf.intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    mm/memory-failure.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/mm/memory-failure.c b/mm/memory-failure.c
    index d3ed748..0af800c 100644
    --- a/mm/memory-failure.c
    +++ b/mm/memory-failure.c
    @@ -208,9 +208,9 @@ static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
    #endif
    si.si_addr_lsb = compound_trans_order(compound_head(page)) + PAGE_SHIFT;

    - if ((flags & MF_ACTION_REQUIRED) && t == current) {
    + if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {
    si.si_code = BUS_MCEERR_AR;
    - ret = force_sig_info(SIGBUS, &si, t);
    + ret = force_sig_info(SIGBUS, &si, current);
    } else {
    /*
    * Don't use force here, it's convenient if the signal
    --
    1.9.1


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