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

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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: edbe83ab4c ("md/raid5: allow the stripe_cache to grow and shrink.")
Cc: stable@vger.kernel.org (4.1 - please release with 2d5b569b66)
Reported-by: Tomas Papan <tomas.papan@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.com>
This commit is contained in:
NeilBrown 2015-08-03 17:09:57 +10:00
parent b6878d9e03
commit 49895bcc7e
1 changed files with 3 additions and 2 deletions
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5
drivers/md/raid5.c
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@ -2256,7 +2256,7 @@ 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);
@ -6388,7 +6388,8 @@ 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;