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    Subject[patch 14/69] oom: fix constraint deadlock
    -stable review patch.  If anyone has any objections, please let us know.
    ---------------------

    From: David Rientjes <rientjes@google.com>

    Fixes a deadlock in the OOM killer for allocations that are not
    __GFP_HARDWALL.

    Before the OOM killer checks for the allocation constraint, it takes
    callback_mutex.

    constrained_alloc() iterates through each zone in the allocation zonelist
    and calls cpuset_zone_allowed_softwall() to determine whether an allocation
    for gfp_mask is possible. If a zone's node is not in the OOM-triggering
    task's mems_allowed, it is not exiting, and we did not fail on a
    __GFP_HARDWALL allocation, cpuset_zone_allowed_softwall() attempts to take
    callback_mutex to check the nearest exclusive ancestor of current's cpuset.
    This results in deadlock.

    We now take callback_mutex after iterating through the zonelist since we
    don't need it yet.

    Cc: Andi Kleen <ak@suse.de>
    Cc: Nick Piggin <npiggin@suse.de>
    Cc: Christoph Lameter <clameter@engr.sgi.com>
    Cc: Martin J. Bligh <mbligh@mbligh.org>
    Signed-off-by: David Rientjes <rientjes@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Chris Wright <chrisw@sous-sol.org>
    ---

    mm/oom_kill.c | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- linux-2.6.21.1.orig/mm/oom_kill.c
    +++ linux-2.6.21.1/mm/oom_kill.c
    @@ -397,6 +397,7 @@ void out_of_memory(struct zonelist *zone
    struct task_struct *p;
    unsigned long points = 0;
    unsigned long freed = 0;
    + int constraint;

    blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
    if (freed > 0)
    @@ -411,14 +412,15 @@ void out_of_memory(struct zonelist *zone
    show_mem();
    }

    - cpuset_lock();
    - read_lock(&tasklist_lock);
    -
    /*
    * Check if there were limitations on the allocation (only relevant for
    * NUMA) that may require different handling.
    */
    - switch (constrained_alloc(zonelist, gfp_mask)) {
    + constraint = constrained_alloc(zonelist, gfp_mask);
    + cpuset_lock();
    + read_lock(&tasklist_lock);
    +
    + switch (constraint) {
    case CONSTRAINT_MEMORY_POLICY:
    oom_kill_process(current, points,
    "No available memory (MPOL_BIND)");
    --
    -
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