BMC/Intel-BMC/linux.git/fs/dax.c, branch dev-4.10

mm: fix data corruption due to stale mmap reads

2017-05-20T12:31:02+00:00

commit cd656375f94632d7b5af57bf67b7b5c0270c591c upstream. Currently, we didn't invalidate page tables during invalidate_inode_pages2() for DAX. That could result in e.g. 2MiB zero page being mapped into page tables while there were already underlying blocks allocated and thus data seen through mmap were different from data seen by read(2). The following sequence reproduces the problem: - open an mmap over a 2MiB hole - read from a 2MiB hole, faulting in a 2MiB zero page - write to the hole with write(3p). The write succeeds but we incorrectly leave the 2MiB zero page mapping intact. - via the mmap, read the data that was just written. Since the zero page mapping is still intact we read back zeroes instead of the new data. Fix the problem by unconditionally calling invalidate_inode_pages2_range() in dax_iomap_actor() for new block allocations and by properly invalidating page tables in invalidate_inode_pages2_range() for DAX mappings. Fixes: c6dcf52c23d2d3fb5235cec42d7dd3f786b87d55 Link: http://lkml.kernel.org/r/20170510085419.27601-3-jack@suse.cz Signed-off-by: Jan Kara Signed-off-by: Ross Zwisler Cc: Dan Williams Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

dax: prevent invalidation of mapped DAX entries

2017-05-20T12:31:02+00:00

commit 4636e70bb0a8b871998b6841a2e4b205cf2bc863 upstream. Patch series "mm,dax: Fix data corruption due to mmap inconsistency", v4. This series fixes data corruption that can happen for DAX mounts when page faults race with write(2) and as a result page tables get out of sync with block mappings in the filesystem and thus data seen through mmap is different from data seen through read(2). The series passes testing with t_mmap_stale test program from Ross and also other mmap related tests on DAX filesystem. This patch (of 4): dax_invalidate_mapping_entry() currently removes DAX exceptional entries only if they are clean and unlocked. This is done via: invalidate_mapping_pages() invalidate_exceptional_entry() dax_invalidate_mapping_entry() However, for page cache pages removed in invalidate_mapping_pages() there is an additional criteria which is that the page must not be mapped. This is noted in the comments above invalidate_mapping_pages() and is checked in invalidate_inode_page(). For DAX entries this means that we can can end up in a situation where a DAX exceptional entry, either a huge zero page or a regular DAX entry, could end up mapped but without an associated radix tree entry. This is inconsistent with the rest of the DAX code and with what happens in the page cache case. We aren't able to unmap the DAX exceptional entry because according to its comments invalidate_mapping_pages() isn't allowed to block, and unmap_mapping_range() takes a write lock on the mapping->i_mmap_rwsem. Since we essentially never have unmapped DAX entries to evict from the radix tree, just remove dax_invalidate_mapping_entry(). Fixes: c6dcf52c23d2 ("mm: Invalidate DAX radix tree entries only if appropriate") Link: http://lkml.kernel.org/r/20170510085419.27601-2-jack@suse.cz Signed-off-by: Ross Zwisler Signed-off-by: Jan Kara Reported-by: Jan Kara Cc: Dan Williams Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

dax: fix radix tree insertion race

2017-04-12T10:42:05+00:00

commit e11f8b7b6c4ea13bf8af6b8f42b45e15b554a92b upstream. While running generic/340 in my test setup I hit the following race. It can happen with kernels that support FS DAX PMDs, so v4.10 thru v4.11-rc5. Thread 1 Thread 2 -------- -------- dax_iomap_pmd_fault() grab_mapping_entry() spin_lock_irq() get_unlocked_mapping_entry() 'entry' is NULL, can't call lock_slot() spin_unlock_irq() radix_tree_preload() dax_iomap_pmd_fault() grab_mapping_entry() spin_lock_irq() get_unlocked_mapping_entry() ... lock_slot() spin_unlock_irq() dax_pmd_insert_mapping() spin_lock_irq() __radix_tree_insert() fails with -EEXIST The issue is that we have to drop mapping->tree_lock while calling radix_tree_preload(), but since we didn't have a radix tree entry to lock (unlike in the pmd_downgrade case) we have no protection against Thread 2 coming along and inserting a PMD at the same index. For 4k entries we handled this with a special-case response to -EEXIST coming from the __radix_tree_insert(), but this doesn't save us for PMDs because the -EEXIST case can also mean that we collided with a 4k entry in the radix tree at a different index, but one that is covered by our PMD range. So, correctly handle both the 4k and 2M collision cases by explicitly re-checking the radix tree for an entry at our index once we reacquire mapping->tree_lock. This patch has made it through a clean xfstests run with the current v4.11-rc5 based linux/master, and it also ran generic/340 500 times in a loop. It used to fail within the first 10 iterations. Link: http://lkml.kernel.org/r/20170406212944.2866-1-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler Cc: "Darrick J. Wong" Cc: Alexander Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Jan Kara Cc: Matthew Wilcox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

fs: break out of iomap_file_buffered_write on fatal signals

2017-02-03T22:13:19+00:00

Tetsuo has noticed that an OOM stress test which performs large write requests can cause the full memory reserves depletion. He has tracked this down to the following path __alloc_pages_nodemask+0x436/0x4d0 alloc_pages_current+0x97/0x1b0 __page_cache_alloc+0x15d/0x1a0 mm/filemap.c:728 pagecache_get_page+0x5a/0x2b0 mm/filemap.c:1331 grab_cache_page_write_begin+0x23/0x40 mm/filemap.c:2773 iomap_write_begin+0x50/0xd0 fs/iomap.c:118 iomap_write_actor+0xb5/0x1a0 fs/iomap.c:190 ? iomap_write_end+0x80/0x80 fs/iomap.c:150 iomap_apply+0xb3/0x130 fs/iomap.c:79 iomap_file_buffered_write+0x68/0xa0 fs/iomap.c:243 ? iomap_write_end+0x80/0x80 xfs_file_buffered_aio_write+0x132/0x390 [xfs] ? remove_wait_queue+0x59/0x60 xfs_file_write_iter+0x90/0x130 [xfs] __vfs_write+0xe5/0x140 vfs_write+0xc7/0x1f0 ? syscall_trace_enter+0x1d0/0x380 SyS_write+0x58/0xc0 do_syscall_64+0x6c/0x200 entry_SYSCALL64_slow_path+0x25/0x25 the oom victim has access to all memory reserves to make a forward progress to exit easier. But iomap_file_buffered_write and other callers of iomap_apply loop to complete the full request. We need to check for fatal signals and back off with a short write instead. As the iomap_apply delegates all the work down to the actor we have to hook into those. All callers that work with the page cache are calling iomap_write_begin so we will check for signals there. dax_iomap_actor has to handle the situation explicitly because it copies data to the userspace directly. Other callers like iomap_page_mkwrite work on a single page or iomap_fiemap_actor do not allocate memory based on the given len. Fixes: 68a9f5e7007c ("xfs: implement iomap based buffered write path") Link: http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@kernel.org Signed-off-by: Michal Hocko Reported-by: Tetsuo Handa Reviewed-by: Christoph Hellwig Cc: Al Viro Cc: [4.8+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

dax: fix build warnings with FS_DAX and !FS_IOMAP

2017-01-25T00:26:14+00:00

As reported by Arnd: https://lkml.org/lkml/2017/1/10/756 Compiling with the following configuration: # CONFIG_EXT2_FS is not set # CONFIG_EXT4_FS is not set # CONFIG_XFS_FS is not set # CONFIG_FS_IOMAP depends on the above filesystems, as is not set CONFIG_FS_DAX=y generates build warnings about unused functions in fs/dax.c: fs/dax.c:878:12: warning: `dax_insert_mapping' defined but not used [-Wunused-function] static int dax_insert_mapping(struct address_space *mapping, ^~~~~~~~~~~~~~~~~~ fs/dax.c:572:12: warning: `copy_user_dax' defined but not used [-Wunused-function] static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size, ^~~~~~~~~~~~~ fs/dax.c:542:12: warning: `dax_load_hole' defined but not used [-Wunused-function] static int dax_load_hole(struct address_space *mapping, void **entry, ^~~~~~~~~~~~~ fs/dax.c:312:14: warning: `grab_mapping_entry' defined but not used [-Wunused-function] static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index, ^~~~~~~~~~~~~~~~~~ Now that the struct buffer_head based DAX fault paths and I/O path have been removed we really depend on iomap support being present for DAX. Make this explicit by selecting FS_IOMAP if we compile in DAX support. This allows us to remove conditional selections of FS_IOMAP when FS_DAX was present for ext2 and ext4, and to remove an #ifdef in fs/dax.c. Link: http://lkml.kernel.org/r/1484087383-29478-1-git-send-email-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler Reported-by: Arnd Bergmann Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

dax: wrprotect pmd_t in dax_mapping_entry_mkclean

2017-01-11T02:31:54+00:00

Currently dax_mapping_entry_mkclean() fails to clean and write protect the pmd_t of a DAX PMD entry during an *sync operation. This can result in data loss in the following sequence: 1) mmap write to DAX PMD, dirtying PMD radix tree entry and making the pmd_t dirty and writeable 2) fsync, flushing out PMD data and cleaning the radix tree entry. We currently fail to mark the pmd_t as clean and write protected. 3) more mmap writes to the PMD. These don't cause any page faults since the pmd_t is dirty and writeable. The radix tree entry remains clean. 4) fsync, which fails to flush the dirty PMD data because the radix tree entry was clean. 5) crash - dirty data that should have been fsync'd as part of 4) could still have been in the processor cache, and is lost. Fix this by marking the pmd_t clean and write protected in dax_mapping_entry_mkclean(), which is called as part of the fsync operation 2). This will cause the writes in step 3) above to generate page faults where we'll re-dirty the PMD radix tree entry, resulting in flushes in the fsync that happens in step 4). Fixes: 4b4bb46d00b3 ("dax: clear dirty entry tags on cache flush") Link: http://lkml.kernel.org/r/1482272586-21177-3-git-send-email-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler Reviewed-by: Jan Kara Cc: Alexander Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Dave Chinner Cc: Jan Kara Cc: Matthew Wilcox Cc: Dave Hansen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

dax: Call ->iomap_begin without entry lock during dax fault

2016-12-27T04:29:25+00:00

Currently ->iomap_begin() handler is called with entry lock held. If the filesystem held any locks between ->iomap_begin() and ->iomap_end() (such as ext4 which will want to hold transaction open), this would cause lock inversion with the iomap_apply() from standard IO path which first calls ->iomap_begin() and only then calls ->actor() callback which grabs entry locks for DAX (if it faults when copying from/to user provided buffers). Fix the problem by nesting grabbing of entry lock inside ->iomap_begin() - ->iomap_end() pair. Reviewed-by: Ross Zwisler Signed-off-by: Jan Kara Signed-off-by: Dan Williams

dax: Finish fault completely when loading holes

2016-12-27T04:29:25+00:00

The only case when we do not finish the page fault completely is when we are loading hole pages into a radix tree. Avoid this special case and finish the fault in that case as well inside the DAX fault handler. It will allow us for easier iomap handling. Reviewed-by: Ross Zwisler Signed-off-by: Jan Kara Signed-off-by: Dan Williams

dax: Avoid page invalidation races and unnecessary radix tree traversals

2016-12-27T04:29:24+00:00

Currently dax_iomap_rw() takes care of invalidating page tables and evicting hole pages from the radix tree when write(2) to the file happens. This invalidation is only necessary when there is some block allocation resulting from write(2). Furthermore in current place the invalidation is racy wrt page fault instantiating a hole page just after we have invalidated it. So perform the page invalidation inside dax_iomap_actor() where we can do it only when really necessary and after blocks have been allocated so nobody will be instantiating new hole pages anymore. Reviewed-by: Christoph Hellwig Reviewed-by: Ross Zwisler Signed-off-by: Jan Kara Signed-off-by: Dan Williams

mm: Invalidate DAX radix tree entries only if appropriate

2016-12-27T04:29:24+00:00

Currently invalidate_inode_pages2_range() and invalidate_mapping_pages() just delete all exceptional radix tree entries they find. For DAX this is not desirable as we track cache dirtiness in these entries and when they are evicted, we may not flush caches although it is necessary. This can for example manifest when we write to the same block both via mmap and via write(2) (to different offsets) and fsync(2) then does not properly flush CPU caches when modification via write(2) was the last one. Create appropriate DAX functions to handle invalidation of DAX entries for invalidate_inode_pages2_range() and invalidate_mapping_pages() and wire them up into the corresponding mm functions. Acked-by: Johannes Weiner Reviewed-by: Ross Zwisler Signed-off-by: Jan Kara Signed-off-by: Dan Williams