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    Subject[PATCH 3.4 38/45] slab/mempolicy: always use local policy from interrupt context
    Date
    From: Andi Kleen <ak@linux.intel.com>

    3.4.104-rc1 review patch. If anyone has any objections, please let me know.

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

    commit e7b691b085fda913830e5280ae6f724b2a63c824 upstream.

    slab_node() could access current->mempolicy from interrupt context.
    However there's a race condition during exit where the mempolicy
    is first freed and then the pointer zeroed.

    Using this from interrupts seems bogus anyways. The interrupt
    will interrupt a random process and therefore get a random
    mempolicy. Many times, this will be idle's, which noone can change.

    Just disable this here and always use local for slab
    from interrupts. I also cleaned up the callers of slab_node a bit
    which always passed the same argument.

    I believe the original mempolicy code did that in fact,
    so it's likely a regression.

    v2: send version with correct logic
    v3: simplify. fix typo.
    Reported-by: Arun Sharma <asharma@fb.com>
    Cc: penberg@kernel.org
    Cc: cl@linux.com
    Signed-off-by: Andi Kleen <ak@linux.intel.com>
    [tdmackey@twitter.com: Rework control flow based on feedback from
    cl@linux.com, fix logic, and cleanup current task_struct reference]
    Acked-by: David Rientjes <rientjes@google.com>
    Acked-by: Christoph Lameter <cl@linux.com>
    Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: David Mackey <tdmackey@twitter.com>
    Signed-off-by: Pekka Enberg <penberg@kernel.org>
    Signed-off-by: Zefan Li <lizefan@huawei.com>
    ---
    include/linux/mempolicy.h | 2 +-
    mm/mempolicy.c | 8 +++++++-
    mm/slab.c | 4 ++--
    mm/slub.c | 2 +-
    4 files changed, 11 insertions(+), 5 deletions(-)

    diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
    index fe07e5a..cc49b23 100644
    --- a/include/linux/mempolicy.h
    +++ b/include/linux/mempolicy.h
    @@ -205,7 +205,7 @@ extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
    extern bool init_nodemask_of_mempolicy(nodemask_t *mask);
    extern bool mempolicy_nodemask_intersects(struct task_struct *tsk,
    const nodemask_t *mask);
    -extern unsigned slab_node(struct mempolicy *policy);
    +extern unsigned slab_node(void);

    extern enum zone_type policy_zone;

    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index 5cec36b..87a43cc 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -1609,8 +1609,14 @@ static unsigned interleave_nodes(struct mempolicy *policy)
    * task can change it's policy. The system default policy requires no
    * such protection.
    */
    -unsigned slab_node(struct mempolicy *policy)
    +unsigned slab_node(void)
    {
    + struct mempolicy *policy;
    +
    + if (in_interrupt())
    + return numa_node_id();
    +
    + policy = current->mempolicy;
    if (!policy || policy->flags & MPOL_F_LOCAL)
    return numa_node_id();

    diff --git a/mm/slab.c b/mm/slab.c
    index da2bb68..3eb1c38 100644
    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -3336,7 +3336,7 @@ static void *alternate_node_alloc(struct kmem_cache *cachep, gfp_t flags)
    if (cpuset_do_slab_mem_spread() && (cachep->flags & SLAB_MEM_SPREAD))
    nid_alloc = cpuset_slab_spread_node();
    else if (current->mempolicy)
    - nid_alloc = slab_node(current->mempolicy);
    + nid_alloc = slab_node();
    if (nid_alloc != nid_here)
    return ____cache_alloc_node(cachep, flags, nid_alloc);
    return NULL;
    @@ -3368,7 +3368,7 @@ static void *fallback_alloc(struct kmem_cache *cache, gfp_t flags)

    retry_cpuset:
    cpuset_mems_cookie = get_mems_allowed();
    - zonelist = node_zonelist(slab_node(current->mempolicy), flags);
    + zonelist = node_zonelist(slab_node(), flags);

    retry:
    /*
    diff --git a/mm/slub.c b/mm/slub.c
    index c6f225f..54ac6e9 100644
    --- a/mm/slub.c
    +++ b/mm/slub.c
    @@ -1617,7 +1617,7 @@ static struct page *get_any_partial(struct kmem_cache *s, gfp_t flags,

    do {
    cpuset_mems_cookie = get_mems_allowed();
    - zonelist = node_zonelist(slab_node(current->mempolicy), flags);
    + zonelist = node_zonelist(slab_node(), flags);
    for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
    struct kmem_cache_node *n;

    --
    1.7.9.5


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