From c93db7bb6ef3251e0ea48ade311d3e9942748e1c Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Tue, 27 Nov 2018 13:16:33 -0800 Subject: dax: Check page->mapping isn't NULL If we race with inode destroy, it's possible for page->mapping to be NULL before we even enter this routine, as well as after having slept waiting for the dax entry to become unlocked. Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()") Cc: Reported-by: Jan Kara Signed-off-by: Matthew Wilcox Reviewed-by: Johannes Thumshirn Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/dax.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index 9bcce89ea18e..e69fc231833b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -365,7 +365,7 @@ bool dax_lock_mapping_entry(struct page *page) struct address_space *mapping = READ_ONCE(page->mapping); locked = false; - if (!dax_mapping(mapping)) + if (!mapping || !dax_mapping(mapping)) break; /* -- cgit v1.2.3 From 55e56f06ed71d9441f3abd5b1d3c1a870812b3fe Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Tue, 27 Nov 2018 13:16:34 -0800 Subject: dax: Don't access a freed inode After we drop the i_pages lock, the inode can be freed at any time. The get_unlocked_entry() code has no choice but to reacquire the lock, so it can't be used here. Create a new wait_entry_unlocked() which takes care not to acquire the lock or dereference the address_space in any way. Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()") Cc: Signed-off-by: Matthew Wilcox Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/dax.c | 32 +++++++++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index e69fc231833b..3f592dc18d67 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -232,6 +232,34 @@ static void *get_unlocked_entry(struct xa_state *xas) } } +/* + * The only thing keeping the address space around is the i_pages lock + * (it's cycled in clear_inode() after removing the entries from i_pages) + * After we call xas_unlock_irq(), we cannot touch xas->xa. + */ +static void wait_entry_unlocked(struct xa_state *xas, void *entry) +{ + struct wait_exceptional_entry_queue ewait; + wait_queue_head_t *wq; + + init_wait(&ewait.wait); + ewait.wait.func = wake_exceptional_entry_func; + + wq = dax_entry_waitqueue(xas, entry, &ewait.key); + prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE); + xas_unlock_irq(xas); + schedule(); + finish_wait(wq, &ewait.wait); + + /* + * Entry lock waits are exclusive. Wake up the next waiter since + * we aren't sure we will acquire the entry lock and thus wake + * the next waiter up on unlock. + */ + if (waitqueue_active(wq)) + __wake_up(wq, TASK_NORMAL, 1, &ewait.key); +} + static void put_unlocked_entry(struct xa_state *xas, void *entry) { /* If we were the only waiter woken, wake the next one */ @@ -389,9 +417,7 @@ bool dax_lock_mapping_entry(struct page *page) entry = xas_load(&xas); if (dax_is_locked(entry)) { rcu_read_unlock(); - entry = get_unlocked_entry(&xas); - xas_unlock_irq(&xas); - put_unlocked_entry(&xas, entry); + wait_entry_unlocked(&xas, entry); rcu_read_lock(); continue; } -- cgit v1.2.3 From 27359fd6e5f3c5db8fe544b63238b6170e8806d8 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 30 Nov 2018 11:05:06 -0500 Subject: dax: Fix unlock mismatch with updated API Internal to dax_unlock_mapping_entry(), dax_unlock_entry() is used to store a replacement entry in the Xarray at the given xas-index with the DAX_LOCKED bit clear. When called, dax_unlock_entry() expects the unlocked value of the entry relative to the current Xarray state to be specified. In most contexts dax_unlock_entry() is operating in the same scope as the matched dax_lock_entry(). However, in the dax_unlock_mapping_entry() case the implementation needs to recall the original entry. In the case where the original entry is a 'pmd' entry it is possible that the pfn performed to do the lookup is misaligned to the value retrieved in the Xarray. Change the api to return the unlock cookie from dax_lock_page() and pass it to dax_unlock_page(). This fixes a bug where dax_unlock_page() was assuming that the page was PMD-aligned if the entry was a PMD entry with signatures like: WARNING: CPU: 38 PID: 1396 at fs/dax.c:340 dax_insert_entry+0x2b2/0x2d0 RIP: 0010:dax_insert_entry+0x2b2/0x2d0 [..] Call Trace: dax_iomap_pte_fault.isra.41+0x791/0xde0 ext4_dax_huge_fault+0x16f/0x1f0 ? up_read+0x1c/0xa0 __do_fault+0x1f/0x160 __handle_mm_fault+0x1033/0x1490 handle_mm_fault+0x18b/0x3d0 Link: https://lkml.kernel.org/r/20181130154902.GL10377@bombadil.infradead.org Fixes: 9f32d221301c ("dax: Convert dax_lock_mapping_entry to XArray") Reported-by: Dan Williams Signed-off-by: Matthew Wilcox Tested-by: Dan Williams Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/dax.c | 21 ++++++++------------- include/linux/dax.h | 14 ++++++++------ mm/memory-failure.c | 6 ++++-- 3 files changed, 20 insertions(+), 21 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 3f592dc18d67..48132eca3761 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -379,20 +379,20 @@ static struct page *dax_busy_page(void *entry) * @page: The page whose entry we want to lock * * Context: Process context. - * Return: %true if the entry was locked or does not need to be locked. + * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could + * not be locked. */ -bool dax_lock_mapping_entry(struct page *page) +dax_entry_t dax_lock_page(struct page *page) { XA_STATE(xas, NULL, 0); void *entry; - bool locked; /* Ensure page->mapping isn't freed while we look at it */ rcu_read_lock(); for (;;) { struct address_space *mapping = READ_ONCE(page->mapping); - locked = false; + entry = NULL; if (!mapping || !dax_mapping(mapping)) break; @@ -403,7 +403,7 @@ bool dax_lock_mapping_entry(struct page *page) * otherwise we would not have a valid pfn_to_page() * translation. */ - locked = true; + entry = (void *)~0UL; if (S_ISCHR(mapping->host->i_mode)) break; @@ -426,23 +426,18 @@ bool dax_lock_mapping_entry(struct page *page) break; } rcu_read_unlock(); - return locked; + return (dax_entry_t)entry; } -void dax_unlock_mapping_entry(struct page *page) +void dax_unlock_page(struct page *page, dax_entry_t cookie) { struct address_space *mapping = page->mapping; XA_STATE(xas, &mapping->i_pages, page->index); - void *entry; if (S_ISCHR(mapping->host->i_mode)) return; - rcu_read_lock(); - entry = xas_load(&xas); - rcu_read_unlock(); - entry = dax_make_entry(page_to_pfn_t(page), dax_is_pmd_entry(entry)); - dax_unlock_entry(&xas, entry); + dax_unlock_entry(&xas, (void *)cookie); } /* diff --git a/include/linux/dax.h b/include/linux/dax.h index 450b28db9533..0dd316a74a29 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -7,6 +7,8 @@ #include #include +typedef unsigned long dax_entry_t; + struct iomap_ops; struct dax_device; struct dax_operations { @@ -88,8 +90,8 @@ 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); +dax_entry_t dax_lock_page(struct page *page); +void dax_unlock_page(struct page *page, dax_entry_t cookie); #else static inline bool bdev_dax_supported(struct block_device *bdev, int blocksize) @@ -122,14 +124,14 @@ static inline int dax_writeback_mapping_range(struct address_space *mapping, return -EOPNOTSUPP; } -static inline bool dax_lock_mapping_entry(struct page *page) +static inline dax_entry_t dax_lock_page(struct page *page) { if (IS_DAX(page->mapping->host)) - return true; - return false; + return ~0UL; + return 0; } -static inline void dax_unlock_mapping_entry(struct page *page) +static inline void dax_unlock_page(struct page *page, dax_entry_t cookie) { } #endif diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 0cd3de3550f0..7c72f2a95785 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1161,6 +1161,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags, LIST_HEAD(tokill); int rc = -EBUSY; loff_t start; + dax_entry_t cookie; /* * Prevent the inode from being freed while we are interrogating @@ -1169,7 +1170,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags, * also prevents changes to the mapping of this pfn until * poison signaling is complete. */ - if (!dax_lock_mapping_entry(page)) + cookie = dax_lock_page(page); + if (!cookie) goto out; if (hwpoison_filter(page)) { @@ -1220,7 +1222,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags, kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags); rc = 0; unlock: - dax_unlock_mapping_entry(page); + dax_unlock_page(page, cookie); out: /* drop pgmap ref acquired in caller */ put_dev_pagemap(pgmap); -- cgit v1.2.3