From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH v6] filesystem-dax: Introduce dax_lock_mapping_entry() From: Dan Williams To: linux-nvdimm@lists.01.org Cc: jack@suse.cz, hch@lst.de, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Date: Wed, 04 Jul 2018 20:33:52 -0700 Message-ID: <153076161392.9314.16967170107658011515.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <153074046078.27838.5465590228767136915.stgit@dwillia2-desk3.amr.corp.intel.com> References: <153074046078.27838.5465590228767136915.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: In preparation for implementing support for memory poison (media error) handling via dax mappings, implement a lock_page() equivalent. Poison error handling requires rmap and needs guarantees that the page->mapping association is maintained / valid (inode not freed) for the duration of the lookup. In the device-dax case it is sufficient to simply hold a dev_pagemap reference. In the filesystem-dax case we need to use the entry lock. Export the entry lock via dax_lock_mapping_entry() that uses rcu_read_lock() to protect against the inode being freed, and revalidates the page->mapping association under xa_lock(). Signed-off-by: Dan Williams --- Changes since v5, fixup kbuild robot reports. fs/dax.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++--- include/linux/dax.h | 13 ++++++ 2 files changed, 116 insertions(+), 6 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 4de11ed463ce..57ec272038da 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -226,8 +226,8 @@ static inline void *unlock_slot(struct address_space *mapping, void **slot) * * Must be called with the i_pages lock held. */ -static void *get_unlocked_mapping_entry(struct address_space *mapping, - pgoff_t index, void ***slotp) +static void *__get_unlocked_mapping_entry(struct address_space *mapping, + pgoff_t index, void ***slotp, bool (*wait_fn)(void)) { void *entry, **slot; struct wait_exceptional_entry_queue ewait; @@ -237,6 +237,8 @@ static void *get_unlocked_mapping_entry(struct address_space *mapping, ewait.wait.func = wake_exceptional_entry_func; for (;;) { + bool revalidate; + entry = __radix_tree_lookup(&mapping->i_pages, index, NULL, &slot); if (!entry || @@ -251,14 +253,31 @@ static void *get_unlocked_mapping_entry(struct address_space *mapping, prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE); xa_unlock_irq(&mapping->i_pages); - schedule(); + revalidate = wait_fn(); finish_wait(wq, &ewait.wait); xa_lock_irq(&mapping->i_pages); + if (revalidate) + return ERR_PTR(-EAGAIN); } } -static void dax_unlock_mapping_entry(struct address_space *mapping, - pgoff_t index) +static bool entry_wait(void) +{ + schedule(); + /* + * Never return an ERR_PTR() from + * __get_unlocked_mapping_entry(), just keep looping. + */ + return false; +} + +static void *get_unlocked_mapping_entry(struct address_space *mapping, + pgoff_t index, void ***slotp) +{ + return __get_unlocked_mapping_entry(mapping, index, slotp, entry_wait); +} + +static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index) { void *entry, **slot; @@ -277,7 +296,7 @@ static void dax_unlock_mapping_entry(struct address_space *mapping, static void put_locked_mapping_entry(struct address_space *mapping, pgoff_t index) { - dax_unlock_mapping_entry(mapping, index); + unlock_mapping_entry(mapping, index); } /* @@ -374,6 +393,84 @@ static struct page *dax_busy_page(void *entry) return NULL; } +static bool entry_wait_revalidate(void) +{ + rcu_read_unlock(); + schedule(); + rcu_read_lock(); + + /* + * Tell __get_unlocked_mapping_entry() to take a break, we need + * to revalidate page->mapping after dropping locks + */ + return true; +} + +bool dax_lock_mapping_entry(struct page *page) +{ + pgoff_t index; + struct inode *inode; + bool did_lock = false; + void *entry = NULL, **slot; + struct address_space *mapping; + + rcu_read_lock(); + for (;;) { + mapping = READ_ONCE(page->mapping); + + if (!dax_mapping(mapping)) + break; + + /* + * In the device-dax case there's no need to lock, a + * struct dev_pagemap pin is sufficient to keep the + * inode alive, and we assume we have dev_pagemap pin + * otherwise we would not have a valid pfn_to_page() + * translation. + */ + inode = mapping->host; + if (S_ISCHR(inode->i_mode)) { + did_lock = true; + break; + } + + xa_lock_irq(&mapping->i_pages); + if (mapping != page->mapping) { + xa_unlock_irq(&mapping->i_pages); + continue; + } + index = page->index; + + entry = __get_unlocked_mapping_entry(mapping, index, &slot, + entry_wait_revalidate); + if (!entry) { + xa_unlock_irq(&mapping->i_pages); + break; + } else if (IS_ERR(entry)) { + WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN); + continue; + } + lock_slot(mapping, slot); + did_lock = true; + xa_unlock_irq(&mapping->i_pages); + break; + } + rcu_read_unlock(); + + return did_lock; +} + +void dax_unlock_mapping_entry(struct page *page) +{ + struct address_space *mapping = page->mapping; + struct inode *inode = mapping->host; + + if (S_ISCHR(inode->i_mode)) + return; + + unlock_mapping_entry(mapping, page->index); +} + /* * Find radix tree entry at given index. If it points to an exceptional entry, * return it with the radix tree entry locked. If the radix tree doesn't diff --git a/include/linux/dax.h b/include/linux/dax.h index deb0f663252f..450b28db9533 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -88,6 +88,8 @@ int dax_writeback_mapping_range(struct address_space *mapping, struct block_device *bdev, struct writeback_control *wbc); struct page *dax_layout_busy_page(struct address_space *mapping); +bool dax_lock_mapping_entry(struct page *page); +void dax_unlock_mapping_entry(struct page *page); #else static inline bool bdev_dax_supported(struct block_device *bdev, int blocksize) @@ -119,6 +121,17 @@ static inline int dax_writeback_mapping_range(struct address_space *mapping, { return -EOPNOTSUPP; } + +static inline bool dax_lock_mapping_entry(struct page *page) +{ + if (IS_DAX(page->mapping->host)) + return true; + return false; +} + +static inline void dax_unlock_mapping_entry(struct page *page) +{ +} #endif int dax_read_lock(void);