From: Vitaly Wool vitaly.wool@konsulko.com Subject: z3fold: simplify freeing slots

Patch series "z3fold: stability / rt fixes".

Address z3fold stability issues under stress load, primarily in the reclaim and free aspects. Besides, it fixes the locking problems that were only seen in real-time kernel configuration.

This patch (of 3):

There used to be two places in the code where slots could be freed, namely when freeing the last allocated handle from the slots and when releasing the z3fold header these slots aree linked to. The logic to decide on whether to free certain slots was complicated and error prone in both functions and it led to failures in RT case.

To fix that, make free_handle() the single point of freeing slots.

Link: https://lkml.kernel.org/r/20201209145151.18994-1-vitaly.wool@konsulko.com Link: https://lkml.kernel.org/r/20201209145151.18994-2-vitaly.wool@konsulko.com Signed-off-by: Vitaly Wool vitaly.wool@konsulko.com Tested-by: Mike Galbraith efault@gmx.de Cc: Sebastian Andrzej Siewior bigeasy@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/z3fold.c | 55 +++++++++++--------------------------------------- 1 file changed, 13 insertions(+), 42 deletions(-)

--- a/mm/z3fold.c~z3fold-simplify-freeing-slots +++ a/mm/z3fold.c @@ -90,7 +90,7 @@ struct z3fold_buddy_slots { * be enough slots to hold all possible variants */ unsigned long slot[BUDDY_MASK + 1]; - unsigned long pool; /* back link + flags */ + unsigned long pool; /* back link */ rwlock_t lock; }; #define HANDLE_FLAG_MASK (0x03) @@ -182,13 +182,6 @@ enum z3fold_page_flags { };

/* - * handle flags, go under HANDLE_FLAG_MASK - */ -enum z3fold_handle_flags { - HANDLES_ORPHANED = 0, -}; - -/* * Forward declarations */ static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool); @@ -303,10 +296,9 @@ static inline void put_z3fold_header(str z3fold_page_unlock(zhdr); }

-static inline void free_handle(unsigned long handle) +static inline void free_handle(unsigned long handle, struct z3fold_header *zhdr) { struct z3fold_buddy_slots *slots; - struct z3fold_header *zhdr; int i; bool is_free;

@@ -316,22 +308,13 @@ static inline void free_handle(unsigned if (WARN_ON(*(unsigned long *)handle == 0)) return;

- zhdr = handle_to_z3fold_header(handle); slots = handle_to_slots(handle); write_lock(&slots->lock); *(unsigned long *)handle = 0; - if (zhdr->slots == slots) { - write_unlock(&slots->lock); - return; /* simple case, nothing else to do */ - } + if (zhdr->slots != slots) + zhdr->foreign_handles--;

- /* we are freeing a foreign handle if we are here */ - zhdr->foreign_handles--; is_free = true; - if (!test_bit(HANDLES_ORPHANED, &slots->pool)) { - write_unlock(&slots->lock); - return; - } for (i = 0; i <= BUDDY_MASK; i++) { if (slots->slot[i]) { is_free = false; @@ -343,6 +326,8 @@ static inline void free_handle(unsigned if (is_free) { struct z3fold_pool *pool = slots_to_pool(slots);

+ if (zhdr->slots == slots) + zhdr->slots = NULL; kmem_cache_free(pool->c_handle, slots); } } @@ -525,8 +510,6 @@ static void __release_z3fold_page(struct { struct page *page = virt_to_page(zhdr); struct z3fold_pool *pool = zhdr_to_pool(zhdr); - bool is_free = true; - int i;

WARN_ON(!list_empty(&zhdr->buddy)); set_bit(PAGE_STALE, &page->private); @@ -536,21 +519,6 @@ static void __release_z3fold_page(struct list_del_init(&page->lru); spin_unlock(&pool->lock);

- /* If there are no foreign handles, free the handles array */ - read_lock(&zhdr->slots->lock); - for (i = 0; i <= BUDDY_MASK; i++) { - if (zhdr->slots->slot[i]) { - is_free = false; - break; - } - } - if (!is_free) - set_bit(HANDLES_ORPHANED, &zhdr->slots->pool); - read_unlock(&zhdr->slots->lock); - - if (is_free) - kmem_cache_free(pool->c_handle, zhdr->slots); - if (locked) z3fold_page_unlock(zhdr);

@@ -973,6 +941,9 @@ lookup: } }

+ if (zhdr && !zhdr->slots) + zhdr->slots = alloc_slots(pool, + can_sleep ? GFP_NOIO : GFP_ATOMIC); return zhdr; }

@@ -1270,7 +1241,7 @@ static void z3fold_free(struct z3fold_po }

if (!page_claimed) - free_handle(handle); + free_handle(handle, zhdr); if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) { atomic64_dec(&pool->pages_nr); return; @@ -1429,19 +1400,19 @@ static int z3fold_reclaim_page(struct z3 ret = pool->ops->evict(pool, middle_handle); if (ret) goto next; - free_handle(middle_handle); + free_handle(middle_handle, zhdr); } if (first_handle) { ret = pool->ops->evict(pool, first_handle); if (ret) goto next; - free_handle(first_handle); + free_handle(first_handle, zhdr); } if (last_handle) { ret = pool->ops->evict(pool, last_handle); if (ret) goto next; - free_handle(last_handle); + free_handle(last_handle, zhdr); } next: if (test_bit(PAGE_HEADLESS, &page->private)) { _