The patch titled Subject: z3fold: stricter locking and more careful reclaim has been added to the -mm tree. Its filename is z3fold-stricter-locking-and-more-careful-reclaim.patch
This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/z3fold-stricter-locking-and-more-c... and later at https://ozlabs.org/~akpm/mmotm/broken-out/z3fold-stricter-locking-and-more-c...
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------------------------------------------------------ From: Vitaly Wool vitaly.wool@konsulko.com Subject: z3fold: stricter locking and more careful reclaim
Use temporary slots in reclaim function to avoid possible race when freeing those.
While at it, make sure we check CLAIMED flag under page lock in the reclaim function to make sure we are not racing with z3fold_alloc().
Link: https://lkml.kernel.org/r/20201209145151.18994-4-vitaly.wool@konsulko.com Signed-off-by: Vitaly Wool vitaly.wool@konsulko.com Cc: stable@vger.kernel.org Cc: Mike Galbraith efault@gmx.de Cc: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/z3fold.c | 143 +++++++++++++++++++++++++++++--------------------- 1 file changed, 85 insertions(+), 58 deletions(-)
--- a/mm/z3fold.c~z3fold-stricter-locking-and-more-careful-reclaim +++ a/mm/z3fold.c @@ -182,6 +182,13 @@ enum z3fold_page_flags { };
/* + * handle flags, go under HANDLE_FLAG_MASK + */ +enum z3fold_handle_flags { + HANDLES_NOFREE = 0, +}; + +/* * Forward declarations */ static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool); @@ -311,6 +318,12 @@ static inline void free_handle(unsigned slots = handle_to_slots(handle); write_lock(&slots->lock); *(unsigned long *)handle = 0; + + if (test_bit(HANDLES_NOFREE, &slots->pool)) { + write_unlock(&slots->lock); + return; /* simple case, nothing else to do */ + } + if (zhdr->slots != slots) zhdr->foreign_handles--;
@@ -621,6 +634,28 @@ static inline void add_to_unbuddied(stru } }
+static inline enum buddy get_free_buddy(struct z3fold_header *zhdr, int chunks) +{ + enum buddy bud = HEADLESS; + + if (zhdr->middle_chunks) { + if (!zhdr->first_chunks && + chunks <= zhdr->start_middle - ZHDR_CHUNKS) + bud = FIRST; + else if (!zhdr->last_chunks) + bud = LAST; + } else { + if (!zhdr->first_chunks) + bud = FIRST; + else if (!zhdr->last_chunks) + bud = LAST; + else + bud = MIDDLE; + } + + return bud; +} + static inline void *mchunk_memmove(struct z3fold_header *zhdr, unsigned short dst_chunk) { @@ -682,18 +717,7 @@ static struct z3fold_header *compact_sin if (WARN_ON(new_zhdr == zhdr)) goto out_fail;
- if (new_zhdr->first_chunks == 0) { - if (new_zhdr->middle_chunks != 0 && - chunks >= new_zhdr->start_middle) { - new_bud = LAST; - } else { - new_bud = FIRST; - } - } else if (new_zhdr->last_chunks == 0) { - new_bud = LAST; - } else if (new_zhdr->middle_chunks == 0) { - new_bud = MIDDLE; - } + new_bud = get_free_buddy(new_zhdr, chunks); q = new_zhdr; switch (new_bud) { case FIRST: @@ -815,9 +839,8 @@ static void do_compact_page(struct z3fol return; }
- if (unlikely(PageIsolated(page) || - test_bit(PAGE_CLAIMED, &page->private) || - test_bit(PAGE_STALE, &page->private))) { + if (test_bit(PAGE_STALE, &page->private) || + test_and_set_bit(PAGE_CLAIMED, &page->private)) { z3fold_page_unlock(zhdr); return; } @@ -826,13 +849,16 @@ static void do_compact_page(struct z3fol zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) { if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) atomic64_dec(&pool->pages_nr); - else + else { + clear_bit(PAGE_CLAIMED, &page->private); z3fold_page_unlock(zhdr); + } return; }
z3fold_compact_page(zhdr); add_to_unbuddied(pool, zhdr); + clear_bit(PAGE_CLAIMED, &page->private); z3fold_page_unlock(zhdr); }
@@ -1080,17 +1106,8 @@ static int z3fold_alloc(struct z3fold_po retry: zhdr = __z3fold_alloc(pool, size, can_sleep); if (zhdr) { - if (zhdr->first_chunks == 0) { - if (zhdr->middle_chunks != 0 && - chunks >= zhdr->start_middle) - bud = LAST; - else - bud = FIRST; - } else if (zhdr->last_chunks == 0) - bud = LAST; - else if (zhdr->middle_chunks == 0) - bud = MIDDLE; - else { + bud = get_free_buddy(zhdr, chunks); + if (bud == HEADLESS) { if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) atomic64_dec(&pool->pages_nr); @@ -1236,7 +1253,6 @@ static void z3fold_free(struct z3fold_po pr_err("%s: unknown bud %d\n", __func__, bud); WARN_ON(1); put_z3fold_header(zhdr); - clear_bit(PAGE_CLAIMED, &page->private); return; }
@@ -1251,8 +1267,7 @@ static void z3fold_free(struct z3fold_po z3fold_page_unlock(zhdr); return; } - if (unlikely(PageIsolated(page)) || - test_and_set_bit(NEEDS_COMPACTING, &page->private)) { + if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) { put_z3fold_header(zhdr); clear_bit(PAGE_CLAIMED, &page->private); return; @@ -1316,6 +1331,10 @@ static int z3fold_reclaim_page(struct z3 struct page *page = NULL; struct list_head *pos; unsigned long first_handle = 0, middle_handle = 0, last_handle = 0; + struct z3fold_buddy_slots slots __attribute__((aligned(SLOTS_ALIGN))); + + rwlock_init(&slots.lock); + slots.pool = (unsigned long)pool | (1 << HANDLES_NOFREE);
spin_lock(&pool->lock); if (!pool->ops || !pool->ops->evict || retries == 0) { @@ -1330,35 +1349,36 @@ static int z3fold_reclaim_page(struct z3 list_for_each_prev(pos, &pool->lru) { page = list_entry(pos, struct page, lru);
- /* this bit could have been set by free, in which case - * we pass over to the next page in the pool. - */ - if (test_and_set_bit(PAGE_CLAIMED, &page->private)) { - page = NULL; - continue; - } - - if (unlikely(PageIsolated(page))) { - clear_bit(PAGE_CLAIMED, &page->private); - page = NULL; - continue; - } zhdr = page_address(page); if (test_bit(PAGE_HEADLESS, &page->private)) break;
+ if (kref_get_unless_zero(&zhdr->refcount) == 0) { + zhdr = NULL; + break; + } if (!z3fold_page_trylock(zhdr)) { - clear_bit(PAGE_CLAIMED, &page->private); + if (kref_put(&zhdr->refcount, + release_z3fold_page)) + atomic64_dec(&pool->pages_nr); zhdr = NULL; continue; /* can't evict at this point */ } - if (zhdr->foreign_handles) { - clear_bit(PAGE_CLAIMED, &page->private); - z3fold_page_unlock(zhdr); + + /* test_and_set_bit is of course atomic, but we still + * need to do it under page lock, otherwise checking + * that bit in __z3fold_alloc wouldn't make sense + */ + if (zhdr->foreign_handles || + test_and_set_bit(PAGE_CLAIMED, &page->private)) { + if (kref_put(&zhdr->refcount, + release_z3fold_page)) + atomic64_dec(&pool->pages_nr); + else + z3fold_page_unlock(zhdr); zhdr = NULL; continue; /* can't evict such page */ } - kref_get(&zhdr->refcount); list_del_init(&zhdr->buddy); zhdr->cpu = -1; break; @@ -1380,12 +1400,16 @@ static int z3fold_reclaim_page(struct z3 first_handle = 0; last_handle = 0; middle_handle = 0; + memset(slots.slot, 0, sizeof(slots.slot)); if (zhdr->first_chunks) - first_handle = encode_handle(zhdr, FIRST); + first_handle = __encode_handle(zhdr, &slots, + FIRST); if (zhdr->middle_chunks) - middle_handle = encode_handle(zhdr, MIDDLE); + middle_handle = __encode_handle(zhdr, &slots, + MIDDLE); if (zhdr->last_chunks) - last_handle = encode_handle(zhdr, LAST); + last_handle = __encode_handle(zhdr, &slots, + LAST); /* * it's safe to unlock here because we hold a * reference to this page @@ -1400,19 +1424,16 @@ static int z3fold_reclaim_page(struct z3 ret = pool->ops->evict(pool, middle_handle); if (ret) goto next; - free_handle(middle_handle, zhdr); } if (first_handle) { ret = pool->ops->evict(pool, first_handle); if (ret) goto next; - free_handle(first_handle, zhdr); } if (last_handle) { ret = pool->ops->evict(pool, last_handle); if (ret) goto next; - free_handle(last_handle, zhdr); } next: if (test_bit(PAGE_HEADLESS, &page->private)) { @@ -1426,9 +1447,11 @@ next: spin_unlock(&pool->lock); clear_bit(PAGE_CLAIMED, &page->private); } else { + struct z3fold_buddy_slots *slots = zhdr->slots; z3fold_page_lock(zhdr); if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) { + kmem_cache_free(pool->c_handle, slots); atomic64_dec(&pool->pages_nr); return 0; } @@ -1544,8 +1567,7 @@ static bool z3fold_page_isolate(struct p VM_BUG_ON_PAGE(!PageMovable(page), page); VM_BUG_ON_PAGE(PageIsolated(page), page);
- if (test_bit(PAGE_HEADLESS, &page->private) || - test_bit(PAGE_CLAIMED, &page->private)) + if (test_bit(PAGE_HEADLESS, &page->private)) return false;
zhdr = page_address(page); @@ -1557,6 +1579,8 @@ static bool z3fold_page_isolate(struct p if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) goto out;
+ if (test_and_set_bit(PAGE_CLAIMED, &page->private)) + goto out; pool = zhdr_to_pool(zhdr); spin_lock(&pool->lock); if (!list_empty(&zhdr->buddy)) @@ -1583,16 +1607,17 @@ static int z3fold_page_migrate(struct ad
VM_BUG_ON_PAGE(!PageMovable(page), page); VM_BUG_ON_PAGE(!PageIsolated(page), page); + VM_BUG_ON_PAGE(!test_bit(PAGE_CLAIMED, &page->private), page); VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
zhdr = page_address(page); pool = zhdr_to_pool(zhdr);
- if (!z3fold_page_trylock(zhdr)) { + if (!z3fold_page_trylock(zhdr)) return -EAGAIN; - } if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) { z3fold_page_unlock(zhdr); + clear_bit(PAGE_CLAIMED, &page->private); return -EBUSY; } if (work_pending(&zhdr->work)) { @@ -1634,6 +1659,7 @@ static int z3fold_page_migrate(struct ad queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
page_mapcount_reset(page); + clear_bit(PAGE_CLAIMED, &page->private); put_page(page); return 0; } @@ -1657,6 +1683,7 @@ static void z3fold_page_putback(struct p spin_lock(&pool->lock); list_add(&page->lru, &pool->lru); spin_unlock(&pool->lock); + clear_bit(PAGE_CLAIMED, &page->private); z3fold_page_unlock(zhdr); }
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Patches currently in -mm which might be from vitaly.wool@konsulko.com are
z3fold-simplify-freeing-slots.patch z3fold-stricter-locking-and-more-careful-reclaim.patch z3fold-remove-preempt-disabled-sections-for-rt.patch