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    Subject[PATCH 4.1 086/159] md/raid5: dont let shrink_slab shrink too far.
    Date
    4.1-stable review patch.  If anyone has any objections, please let me know.

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

    From: NeilBrown <neilb@suse.com>

    commit 49895bcc7e566ba455eb2996607d6fbd3447ce16 upstream.

    I have a report of drop_one_stripe() called from
    raid5_cache_scan() apparently finding ->max_nr_stripes == 0.

    This should not be allowed.

    So add a test to keep max_nr_stripes above min_nr_stripes.

    Also use a 'mask' rather than a 'mod' in drop_one_stripe
    to ensure 'hash' is valid even if max_nr_stripes does reach zero.


    Fixes: edbe83ab4c27 ("md/raid5: allow the stripe_cache to grow and shrink.")
    Reported-by: Tomas Papan <tomas.papan@gmail.com>
    Signed-off-by: NeilBrown <neilb@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/raid5.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/md/raid5.c
    +++ b/drivers/md/raid5.c
    @@ -2245,7 +2245,7 @@ static int resize_stripes(struct r5conf
    static int drop_one_stripe(struct r5conf *conf)
    {
    struct stripe_head *sh;
    - int hash = (conf->max_nr_stripes - 1) % NR_STRIPE_HASH_LOCKS;
    + int hash = (conf->max_nr_stripes - 1) & STRIPE_HASH_LOCKS_MASK;

    spin_lock_irq(conf->hash_locks + hash);
    sh = get_free_stripe(conf, hash);
    @@ -6375,7 +6375,8 @@ static unsigned long raid5_cache_scan(st

    if (mutex_trylock(&conf->cache_size_mutex)) {
    ret= 0;
    - while (ret < sc->nr_to_scan) {
    + while (ret < sc->nr_to_scan &&
    + conf->max_nr_stripes > conf->min_nr_stripes) {
    if (drop_one_stripe(conf) == 0) {
    ret = SHRINK_STOP;
    break;



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