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dkim=pass header.d=bytedance-com.20150623.gappssmtp.com header.s=20150623 header.b=fDKQNUhc; spf=pass (imf23.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.216.44 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 82E419000701 X-Stat-Signature: axgq5w48t5tem83a489pnd5qejxgdtzf X-HE-Tag: 1628918774-133052 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: When we use objcg APIs to charge the LRU pages, the page will not hold a reference to the memcg associated with the page. So the caller of the {folio,page}_memcg() should hold an rcu read lock or obtain a reference to the memcg associated with the page to protect memcg from being released. So introduce get_mem_cgroup_from_{page,folio}() to obtain a reference to the memory cgroup associated with the page. In this patch, make all the callers hold an rcu read lock or obtain a reference to the memcg to protect memcg from being released when the LRU pages reparented. We do not need to adjust the callers of {folio,page}_memcg() during the whole process of mem_cgroup_move_task(). Because the cgroup migration and memory cgroup offlining are serialized by @cgroup_mutex. In this routine, the LRU pages cannot be reparented to its parent memory cgroup. So {folio,page}_memcg() is stable and cannot be released. This is a preparation for reparenting the LRU pages. Signed-off-by: Muchun Song --- fs/buffer.c | 3 ++- fs/fs-writeback.c | 23 +++++++++++---------- include/linux/memcontrol.h | 49 ++++++++++++++++++++++++++++++++++++++++++--- mm/memcontrol.c | 50 ++++++++++++++++++++++++++++++++++++---------- mm/migrate.c | 4 ++++ mm/page_io.c | 5 +++-- 6 files changed, 106 insertions(+), 28 deletions(-) diff --git a/fs/buffer.c b/fs/buffer.c index f5384cff7e0c..88123f84885a 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -823,7 +823,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, gfp |= __GFP_NOFAIL; /* The page lock pins the memcg */ - memcg = page_memcg(page); + memcg = get_mem_cgroup_from_page(page); old_memcg = set_active_memcg(memcg); head = NULL; @@ -843,6 +843,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, set_bh_page(bh, page, offset); } out: + mem_cgroup_put(memcg); set_active_memcg(old_memcg); return head; /* diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 81ec192ce067..d9a67fffcc78 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -243,15 +243,13 @@ void __inode_attach_wb(struct inode *inode, struct page *page) if (inode_cgwb_enabled(inode)) { struct cgroup_subsys_state *memcg_css; - if (page) { - memcg_css = mem_cgroup_css_from_page(page); - wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); - } else { - /* must pin memcg_css, see wb_get_create() */ + /* must pin memcg_css, see wb_get_create() */ + if (page) + memcg_css = get_mem_cgroup_css_from_page(page); + else memcg_css = task_get_css(current, memory_cgrp_id); - wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); - css_put(memcg_css); - } + wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + css_put(memcg_css); } if (!wb) @@ -866,16 +864,16 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page, if (!wbc->wb || wbc->no_cgroup_owner) return; - css = mem_cgroup_css_from_page(page); + css = get_mem_cgroup_css_from_page(page); /* dead cgroups shouldn't contribute to inode ownership arbitration */ if (!(css->flags & CSS_ONLINE)) - return; + goto out; id = css->id; if (id == wbc->wb_id) { wbc->wb_bytes += bytes; - return; + goto out; } if (id == wbc->wb_lcand_id) @@ -888,6 +886,9 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page, wbc->wb_tcand_bytes += bytes; else wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes); + +out: + css_put(css); } EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner); diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 5a8f85bd9bbf..431fc606f6f9 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -378,7 +378,7 @@ static inline bool folio_memcg_kmem(struct folio *folio); * a valid memcg, but can be atomically swapped to the parent memcg. * * The caller must ensure that the returned memcg won't be released: - * e.g. acquire the rcu_read_lock or css_set_lock. + * e.g. acquire the rcu_read_lock or css_set_lock or cgroup_mutex. */ static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg) { @@ -460,6 +460,36 @@ static inline struct mem_cgroup *page_memcg(struct page *page) } /* + * get_mem_cgroup_from_folio - Obtain a reference on the memory cgroup + * associated with a folio. + * @folio: Pointer to the folio. + * + * Returns a pointer to the memory cgroup (and obtain a reference on it) + * associated with the folio, or NULL. This function assumes that the + * folio is known to have a proper memory cgroup pointer. It's not safe + * to call this function against some type of pages, e.g. slab pages or + * ex-slab pages. + */ +static inline struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio) +{ + struct mem_cgroup *memcg; + + rcu_read_lock(); +retry: + memcg = folio_memcg(folio); + if (unlikely(memcg && !css_tryget(&memcg->css))) + goto retry; + rcu_read_unlock(); + + return memcg; +} + +static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) +{ + return get_mem_cgroup_from_folio(page_folio(page)); +} + +/* * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio. * @folio: Pointer to the folio. * @@ -893,7 +923,7 @@ static inline bool mm_match_cgroup(struct mm_struct *mm, return match; } -struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page); +struct cgroup_subsys_state *get_mem_cgroup_css_from_page(struct page *page); ino_t page_cgroup_ino(struct page *page); static inline bool mem_cgroup_online(struct mem_cgroup *memcg) @@ -1051,10 +1081,13 @@ static inline void count_memcg_events(struct mem_cgroup *memcg, static inline void count_memcg_page_event(struct page *page, enum vm_event_item idx) { - struct mem_cgroup *memcg = page_memcg(page); + struct mem_cgroup *memcg; + rcu_read_lock(); + memcg = page_memcg(page); if (memcg) count_memcg_events(memcg, idx, 1); + rcu_read_unlock(); } static inline void count_memcg_event_mm(struct mm_struct *mm, @@ -1133,6 +1166,16 @@ static inline struct mem_cgroup *page_memcg(struct page *page) return NULL; } +static inline struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio) +{ + return NULL; +} + +static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) +{ + return NULL; +} + static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio) { WARN_ON_ONCE(!rcu_read_lock_held()); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7955da38e385..0eca3cf6cede 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -424,7 +424,7 @@ EXPORT_SYMBOL(memcg_kmem_enabled_key); #endif /** - * mem_cgroup_css_from_page - css of the memcg associated with a page + * get_mem_cgroup_css_from_page - get css of the memcg associated with a page * @page: page of interest * * If memcg is bound to the default hierarchy, css of the memcg associated @@ -434,13 +434,15 @@ EXPORT_SYMBOL(memcg_kmem_enabled_key); * If memcg is bound to a traditional hierarchy, the css of root_mem_cgroup * is returned. */ -struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page) +struct cgroup_subsys_state *get_mem_cgroup_css_from_page(struct page *page) { struct mem_cgroup *memcg; - memcg = page_memcg(page); + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) + return &root_mem_cgroup->css; - if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys)) + memcg = get_mem_cgroup_from_page(page); + if (!memcg) memcg = root_mem_cgroup; return &memcg->css; @@ -1983,7 +1985,9 @@ void folio_memcg_lock(struct folio *folio) * The RCU lock is held throughout the transaction. The fast * path can get away without acquiring the memcg->move_lock * because page moving starts with an RCU grace period. - */ + * + * The RCU lock also protects the memcg from being freed. + */ rcu_read_lock(); if (mem_cgroup_disabled()) @@ -4553,7 +4557,7 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages, void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio, struct bdi_writeback *wb) { - struct mem_cgroup *memcg = folio_memcg(folio); + struct mem_cgroup *memcg = get_mem_cgroup_from_folio(folio); struct memcg_cgwb_frn *frn; u64 now = get_jiffies_64(); u64 oldest_at = now; @@ -4600,6 +4604,7 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio, frn->memcg_id = wb->memcg_css->id; frn->at = now; } + css_put(&memcg->css); } /* issue foreign writeback flushes for recorded foreign dirtying events */ @@ -6169,6 +6174,14 @@ static void mem_cgroup_move_charge(void) atomic_dec(&mc.from->moving_account); } +/* + * The cgroup migration and memory cgroup offlining are serialized by + * @cgroup_mutex. If we reach here, it means that the LRU pages cannot + * be reparented to its parent memory cgroup. So during the whole process + * of mem_cgroup_move_task(), page_memcg(page) is stable. So we do not + * need to worry about the memcg (returned from page_memcg()) being + * released even if we do not hold an rcu read lock. + */ static void mem_cgroup_move_task(void) { if (mc.to) { @@ -6991,7 +7004,7 @@ void mem_cgroup_migrate(struct folio *old, struct folio *new) if (folio_memcg(new)) return; - memcg = folio_memcg(old); + memcg = get_mem_cgroup_from_folio(old); VM_WARN_ON_ONCE_FOLIO(!memcg, old); if (!memcg) return; @@ -7010,6 +7023,8 @@ void mem_cgroup_migrate(struct folio *old, struct folio *new) mem_cgroup_charge_statistics(memcg, nr_pages); memcg_check_events(memcg, folio_nid(new)); local_irq_restore(flags); + + css_put(&memcg->css); } DEFINE_STATIC_KEY_FALSE(memcg_sockets_enabled_key); @@ -7198,6 +7213,10 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) return; + /* + * Interrupts should be disabled by the caller (see the comments below), + * which can serve as RCU read-side critical sections. + */ memcg = page_memcg(page); VM_WARN_ON_ONCE_PAGE(!memcg, page); @@ -7262,15 +7281,16 @@ int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry) if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) return 0; + rcu_read_lock(); memcg = page_memcg(page); VM_WARN_ON_ONCE_PAGE(!memcg, page); if (!memcg) - return 0; + goto out; if (!entry.val) { memcg_memory_event(memcg, MEMCG_SWAP_FAIL); - return 0; + goto out; } memcg = mem_cgroup_id_get_online(memcg); @@ -7280,6 +7300,7 @@ int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry) memcg_memory_event(memcg, MEMCG_SWAP_MAX); memcg_memory_event(memcg, MEMCG_SWAP_FAIL); mem_cgroup_id_put(memcg); + rcu_read_unlock(); return -ENOMEM; } @@ -7289,6 +7310,8 @@ int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry) oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg), nr_pages); VM_BUG_ON_PAGE(oldid, page); mod_memcg_state(memcg, MEMCG_SWAP, nr_pages); +out: + rcu_read_unlock(); return 0; } @@ -7343,17 +7366,22 @@ bool mem_cgroup_swap_full(struct page *page) if (cgroup_memory_noswap || !cgroup_subsys_on_dfl(memory_cgrp_subsys)) return false; + rcu_read_lock(); memcg = page_memcg(page); if (!memcg) - return false; + goto out; for (; memcg != root_mem_cgroup; memcg = parent_mem_cgroup(memcg)) { unsigned long usage = page_counter_read(&memcg->swap); if (usage * 2 >= READ_ONCE(memcg->swap.high) || - usage * 2 >= READ_ONCE(memcg->swap.max)) + usage * 2 >= READ_ONCE(memcg->swap.max)) { + rcu_read_unlock(); return true; + } } +out: + rcu_read_unlock(); return false; } diff --git a/mm/migrate.c b/mm/migrate.c index 7a03a61bbcd8..cc7f5ecfd4a2 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -473,6 +473,10 @@ int folio_migrate_mapping(struct address_space *mapping, struct lruvec *old_lruvec, *new_lruvec; struct mem_cgroup *memcg; + /* + * Irq is disabled, which can serve as RCU read-side critical + * sections. + */ memcg = folio_memcg(folio); old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat); new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat); diff --git a/mm/page_io.c b/mm/page_io.c index d597bc6e6e45..63014c61932a 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -269,13 +269,14 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct page *page) struct cgroup_subsys_state *css; struct mem_cgroup *memcg; + rcu_read_lock(); memcg = page_memcg(page); if (!memcg) - return; + goto out; - rcu_read_lock(); css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys); bio_associate_blkg_from_css(bio, css); +out: rcu_read_unlock(); } #else