md/raid5: don't let shrink_slab shrink too far.

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>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index b369cbea4e54b767815dbd8d250aca646d23e119..23af6772f146971cc92e857a2a5fc18f3ee1e83f 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2245,7 +2245,7 @@ static int resize_stripes(struct r5conf *conf, int newsize)
 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(struct shrinker *shrink,
 
        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;