From e568df6b84ff05a22467503afc11bee7a6ba0700 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 10 Aug 2016 16:42:53 +0200 Subject: [PATCH 1/6] ext2: Return BH_New buffers for zeroed blocks So far we did not return BH_New buffers from ext2_get_blocks() when we allocated and zeroed-out a block for DAX inode to avoid racy zeroing in DAX code. This zeroing is gone these days so we can remove the workaround. Reviewed-by: Ross Zwisler Reviewed-by: Christoph Hellwig Signed-off-by: Jan Kara Signed-off-by: Dan Williams --- fs/ext2/inode.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c index 0093ea2512a8..f073bfca694b 100644 --- a/fs/ext2/inode.c +++ b/fs/ext2/inode.c @@ -751,9 +751,8 @@ static int ext2_get_blocks(struct inode *inode, mutex_unlock(&ei->truncate_mutex); goto cleanup; } - } else { - *new = true; } + *new = true; ext2_splice_branch(inode, iblock, partial, indirect_blks, count); mutex_unlock(&ei->truncate_mutex); From c6dcf52c23d2d3fb5235cec42d7dd3f786b87d55 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 10 Aug 2016 17:22:44 +0200 Subject: [PATCH 2/6] mm: Invalidate DAX radix tree entries only if appropriate 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 --- fs/dax.c | 75 +++++++++++++++++++++++++++++++++++++-------- include/linux/dax.h | 3 ++ mm/truncate.c | 75 ++++++++++++++++++++++++++++++++++++--------- 3 files changed, 127 insertions(+), 26 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index a8732fbed381..bcfedd184860 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -451,16 +451,37 @@ void dax_wake_mapping_entry_waiter(struct address_space *mapping, __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key); } +static int __dax_invalidate_mapping_entry(struct address_space *mapping, + pgoff_t index, bool trunc) +{ + int ret = 0; + void *entry; + struct radix_tree_root *page_tree = &mapping->page_tree; + + spin_lock_irq(&mapping->tree_lock); + entry = get_unlocked_mapping_entry(mapping, index, NULL); + if (!entry || !radix_tree_exceptional_entry(entry)) + goto out; + if (!trunc && + (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) || + radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))) + goto out; + radix_tree_delete(page_tree, index); + mapping->nrexceptional--; + ret = 1; +out: + put_unlocked_mapping_entry(mapping, index, entry); + spin_unlock_irq(&mapping->tree_lock); + return ret; +} /* * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree * entry to get unlocked before deleting it. */ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index) { - void *entry; + int ret = __dax_invalidate_mapping_entry(mapping, index, true); - spin_lock_irq(&mapping->tree_lock); - entry = get_unlocked_mapping_entry(mapping, index, NULL); /* * This gets called from truncate / punch_hole path. As such, the caller * must hold locks protecting against concurrent modifications of the @@ -468,16 +489,46 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index) * caller has seen exceptional entry for this index, we better find it * at that index as well... */ - if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) { - spin_unlock_irq(&mapping->tree_lock); - return 0; - } - radix_tree_delete(&mapping->page_tree, index); - mapping->nrexceptional--; - spin_unlock_irq(&mapping->tree_lock); - dax_wake_mapping_entry_waiter(mapping, index, entry, true); + WARN_ON_ONCE(!ret); + return ret; +} - return 1; +/* + * Invalidate exceptional DAX entry if easily possible. This handles DAX + * entries for invalidate_inode_pages() so we evict the entry only if we can + * do so without blocking. + */ +int dax_invalidate_mapping_entry(struct address_space *mapping, pgoff_t index) +{ + int ret = 0; + void *entry, **slot; + struct radix_tree_root *page_tree = &mapping->page_tree; + + spin_lock_irq(&mapping->tree_lock); + entry = __radix_tree_lookup(page_tree, index, NULL, &slot); + if (!entry || !radix_tree_exceptional_entry(entry) || + slot_locked(mapping, slot)) + goto out; + if (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) || + radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)) + goto out; + radix_tree_delete(page_tree, index); + mapping->nrexceptional--; + ret = 1; +out: + spin_unlock_irq(&mapping->tree_lock); + if (ret) + dax_wake_mapping_entry_waiter(mapping, index, entry, true); + return ret; +} + +/* + * Invalidate exceptional DAX entry if it is clean. + */ +int dax_invalidate_mapping_entry_sync(struct address_space *mapping, + pgoff_t index) +{ + return __dax_invalidate_mapping_entry(mapping, index, false); } /* diff --git a/include/linux/dax.h b/include/linux/dax.h index f97bcfe79472..24ad71173995 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -41,6 +41,9 @@ ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter, int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, struct iomap_ops *ops); int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index); +int dax_invalidate_mapping_entry(struct address_space *mapping, pgoff_t index); +int dax_invalidate_mapping_entry_sync(struct address_space *mapping, + pgoff_t index); void dax_wake_mapping_entry_waiter(struct address_space *mapping, pgoff_t index, void *entry, bool wake_all); diff --git a/mm/truncate.c b/mm/truncate.c index fd97f1dbce29..dd7b24e083c5 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -24,20 +24,12 @@ #include #include "internal.h" -static void clear_exceptional_entry(struct address_space *mapping, - pgoff_t index, void *entry) +static void clear_shadow_entry(struct address_space *mapping, pgoff_t index, + void *entry) { struct radix_tree_node *node; void **slot; - /* Handled by shmem itself */ - if (shmem_mapping(mapping)) - return; - - if (dax_mapping(mapping)) { - dax_delete_mapping_entry(mapping, index); - return; - } spin_lock_irq(&mapping->tree_lock); /* * Regular page slots are stabilized by the page lock even @@ -55,6 +47,56 @@ static void clear_exceptional_entry(struct address_space *mapping, spin_unlock_irq(&mapping->tree_lock); } +/* + * Unconditionally remove exceptional entry. Usually called from truncate path. + */ +static void truncate_exceptional_entry(struct address_space *mapping, + pgoff_t index, void *entry) +{ + /* Handled by shmem itself */ + if (shmem_mapping(mapping)) + return; + + if (dax_mapping(mapping)) { + dax_delete_mapping_entry(mapping, index); + return; + } + clear_shadow_entry(mapping, index, entry); +} + +/* + * Invalidate exceptional entry if easily possible. This handles exceptional + * entries for invalidate_inode_pages() so for DAX it evicts only unlocked and + * clean entries. + */ +static int invalidate_exceptional_entry(struct address_space *mapping, + pgoff_t index, void *entry) +{ + /* Handled by shmem itself */ + if (shmem_mapping(mapping)) + return 1; + if (dax_mapping(mapping)) + return dax_invalidate_mapping_entry(mapping, index); + clear_shadow_entry(mapping, index, entry); + return 1; +} + +/* + * Invalidate exceptional entry if clean. This handles exceptional entries for + * invalidate_inode_pages2() so for DAX it evicts only clean entries. + */ +static int invalidate_exceptional_entry2(struct address_space *mapping, + pgoff_t index, void *entry) +{ + /* Handled by shmem itself */ + if (shmem_mapping(mapping)) + return 1; + if (dax_mapping(mapping)) + return dax_invalidate_mapping_entry_sync(mapping, index); + clear_shadow_entry(mapping, index, entry); + return 1; +} + /** * do_invalidatepage - invalidate part or all of a page * @page: the page which is affected @@ -262,7 +304,8 @@ void truncate_inode_pages_range(struct address_space *mapping, break; if (radix_tree_exceptional_entry(page)) { - clear_exceptional_entry(mapping, index, page); + truncate_exceptional_entry(mapping, index, + page); continue; } @@ -351,7 +394,8 @@ void truncate_inode_pages_range(struct address_space *mapping, } if (radix_tree_exceptional_entry(page)) { - clear_exceptional_entry(mapping, index, page); + truncate_exceptional_entry(mapping, index, + page); continue; } @@ -470,7 +514,8 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping, break; if (radix_tree_exceptional_entry(page)) { - clear_exceptional_entry(mapping, index, page); + invalidate_exceptional_entry(mapping, index, + page); continue; } @@ -592,7 +637,9 @@ int invalidate_inode_pages2_range(struct address_space *mapping, break; if (radix_tree_exceptional_entry(page)) { - clear_exceptional_entry(mapping, index, page); + if (!invalidate_exceptional_entry2(mapping, + index, page)) + ret = -EBUSY; continue; } From e3fce68cdbed297d927e993b3ea7b8b1cee545da Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 10 Aug 2016 17:10:28 +0200 Subject: [PATCH 3/6] dax: Avoid page invalidation races and unnecessary radix tree traversals 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 --- fs/dax.c | 28 +++++++++++----------------- 1 file changed, 11 insertions(+), 17 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index bcfedd184860..08e15db28b79 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -985,6 +985,17 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data, if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED)) return -EIO; + /* + * Write can allocate block for an area which has a hole page mapped + * into page tables. We have to tear down these mappings so that data + * written by write(2) is visible in mmap. + */ + if ((iomap->flags & IOMAP_F_NEW) && inode->i_mapping->nrpages) { + invalidate_inode_pages2_range(inode->i_mapping, + pos >> PAGE_SHIFT, + (end - 1) >> PAGE_SHIFT); + } + while (pos < end) { unsigned offset = pos & (PAGE_SIZE - 1); struct blk_dax_ctl dax = { 0 }; @@ -1043,23 +1054,6 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter, if (iov_iter_rw(iter) == WRITE) flags |= IOMAP_WRITE; - /* - * Yes, even DAX files can have page cache attached to them: A zeroed - * page is inserted into the pagecache when we have to serve a write - * fault on a hole. It should never be dirtied and can simply be - * dropped from the pagecache once we get real data for the page. - * - * XXX: This is racy against mmap, and there's nothing we can do about - * it. We'll eventually need to shift this down even further so that - * we can check if we allocated blocks over a hole first. - */ - if (mapping->nrpages) { - ret = invalidate_inode_pages2_range(mapping, - pos >> PAGE_SHIFT, - (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT); - WARN_ON_ONCE(ret); - } - while (iov_iter_count(iter)) { ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops, iter, dax_iomap_actor); From f449b936f1aff7696b24a338f493d5cee8d48d55 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 19 Oct 2016 14:48:38 +0200 Subject: [PATCH 4/6] dax: Finish fault completely when loading holes 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 --- fs/dax.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 08e15db28b79..bfec6f2ef613 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -539,15 +539,16 @@ int dax_invalidate_mapping_entry_sync(struct address_space *mapping, * otherwise it will simply fall out of the page cache under memory * pressure without ever having been dirtied. */ -static int dax_load_hole(struct address_space *mapping, void *entry, +static int dax_load_hole(struct address_space *mapping, void **entry, struct vm_fault *vmf) { struct page *page; + int ret; /* Hole page already exists? Return it... */ - if (!radix_tree_exceptional_entry(entry)) { - vmf->page = entry; - return VM_FAULT_LOCKED; + if (!radix_tree_exceptional_entry(*entry)) { + page = *entry; + goto out; } /* This will replace locked radix tree entry with a hole page */ @@ -555,8 +556,17 @@ static int dax_load_hole(struct address_space *mapping, void *entry, vmf->gfp_mask | __GFP_ZERO); if (!page) return VM_FAULT_OOM; + out: vmf->page = page; - return VM_FAULT_LOCKED; + ret = finish_fault(vmf); + vmf->page = NULL; + *entry = page; + if (!ret) { + /* Grab reference for PTE that is now referencing the page */ + get_page(page); + return VM_FAULT_NOPAGE; + } + return ret; } static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size, @@ -1163,8 +1173,8 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, case IOMAP_UNWRITTEN: case IOMAP_HOLE: if (!(vmf->flags & FAULT_FLAG_WRITE)) { - vmf_ret = dax_load_hole(mapping, entry, vmf); - break; + vmf_ret = dax_load_hole(mapping, &entry, vmf); + goto finish_iomap; } /*FALLTHRU*/ default: @@ -1185,8 +1195,7 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, } } unlock_entry: - if (vmf_ret != VM_FAULT_LOCKED || error) - put_locked_mapping_entry(mapping, vmf->pgoff, entry); + put_locked_mapping_entry(mapping, vmf->pgoff, entry); out: if (error == -ENOMEM) return VM_FAULT_OOM | major; From 9f141d6ef6258a3a37a045842d9ba7e68f368956 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 19 Oct 2016 14:34:31 +0200 Subject: [PATCH 5/6] dax: Call ->iomap_begin without entry lock during dax fault 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 --- fs/dax.c | 123 ++++++++++++++++++++++++++++++------------------------- 1 file changed, 67 insertions(+), 56 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index bfec6f2ef613..5c74f60d0a50 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1078,6 +1078,15 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter, } EXPORT_SYMBOL_GPL(dax_iomap_rw); +static int dax_fault_return(int error) +{ + if (error == 0) + return VM_FAULT_NOPAGE; + if (error == -ENOMEM) + return VM_FAULT_OOM; + return VM_FAULT_SIGBUS; +} + /** * dax_iomap_fault - handle a page fault on a DAX file * @vma: The virtual memory area where the fault occurred @@ -1110,12 +1119,6 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, if (pos >= i_size_read(inode)) return VM_FAULT_SIGBUS; - entry = grab_mapping_entry(mapping, vmf->pgoff, 0); - if (IS_ERR(entry)) { - error = PTR_ERR(entry); - goto out; - } - if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page) flags |= IOMAP_WRITE; @@ -1126,9 +1129,15 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, */ error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap); if (error) - goto unlock_entry; + return dax_fault_return(error); if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) { - error = -EIO; /* fs corruption? */ + vmf_ret = dax_fault_return(-EIO); /* fs corruption? */ + goto finish_iomap; + } + + entry = grab_mapping_entry(mapping, vmf->pgoff, 0); + if (IS_ERR(entry)) { + vmf_ret = dax_fault_return(PTR_ERR(entry)); goto finish_iomap; } @@ -1151,13 +1160,13 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, } if (error) - goto finish_iomap; + goto error_unlock_entry; __SetPageUptodate(vmf->cow_page); vmf_ret = finish_fault(vmf); if (!vmf_ret) vmf_ret = VM_FAULT_DONE_COW; - goto finish_iomap; + goto unlock_entry; } switch (iomap.type) { @@ -1169,12 +1178,15 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, } error = dax_insert_mapping(mapping, iomap.bdev, sector, PAGE_SIZE, &entry, vma, vmf); + /* -EBUSY is fine, somebody else faulted on the same PTE */ + if (error == -EBUSY) + error = 0; break; case IOMAP_UNWRITTEN: case IOMAP_HOLE: if (!(vmf->flags & FAULT_FLAG_WRITE)) { vmf_ret = dax_load_hole(mapping, &entry, vmf); - goto finish_iomap; + goto unlock_entry; } /*FALLTHRU*/ default: @@ -1183,30 +1195,25 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf, break; } - finish_iomap: - if (ops->iomap_end) { - if (error || (vmf_ret & VM_FAULT_ERROR)) { - /* keep previous error */ - ops->iomap_end(inode, pos, PAGE_SIZE, 0, flags, - &iomap); - } else { - error = ops->iomap_end(inode, pos, PAGE_SIZE, - PAGE_SIZE, flags, &iomap); - } - } + error_unlock_entry: + vmf_ret = dax_fault_return(error) | major; unlock_entry: put_locked_mapping_entry(mapping, vmf->pgoff, entry); - out: - if (error == -ENOMEM) - return VM_FAULT_OOM | major; - /* -EBUSY is fine, somebody else faulted on the same PTE */ - if (error < 0 && error != -EBUSY) - return VM_FAULT_SIGBUS | major; - if (vmf_ret) { - WARN_ON_ONCE(error); /* -EBUSY from ops->iomap_end? */ - return vmf_ret; + finish_iomap: + if (ops->iomap_end) { + int copied = PAGE_SIZE; + + if (vmf_ret & VM_FAULT_ERROR) + copied = 0; + /* + * The fault is done by now and there's no way back (other + * thread may be already happily using PTE we have installed). + * Just ignore error from ->iomap_end since we cannot do much + * with it. + */ + ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap); } - return VM_FAULT_NOPAGE | major; + return vmf_ret; } EXPORT_SYMBOL_GPL(dax_iomap_fault); @@ -1330,16 +1337,6 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address, if ((pgoff | PG_PMD_COLOUR) > max_pgoff) goto fallback; - /* - * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX - * PMD or a HZP entry. If it can't (because a 4k page is already in - * the tree, for instance), it will return -EEXIST and we just fall - * back to 4k entries. - */ - entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD); - if (IS_ERR(entry)) - goto fallback; - /* * Note that we don't use iomap_apply here. We aren't doing I/O, only * setting up a mapping, so really we're using iomap_begin() as a way @@ -1348,10 +1345,21 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address, pos = (loff_t)pgoff << PAGE_SHIFT; error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap); if (error) - goto unlock_entry; + goto fallback; + if (iomap.offset + iomap.length < pos + PMD_SIZE) goto finish_iomap; + /* + * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX + * PMD or a HZP entry. If it can't (because a 4k page is already in + * the tree, for instance), it will return -EEXIST and we just fall + * back to 4k entries. + */ + entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD); + if (IS_ERR(entry)) + goto finish_iomap; + vmf.pgoff = pgoff; vmf.flags = flags; vmf.gfp_mask = mapping_gfp_mask(mapping) | __GFP_IO; @@ -1364,7 +1372,7 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address, case IOMAP_UNWRITTEN: case IOMAP_HOLE: if (WARN_ON_ONCE(write)) - goto finish_iomap; + goto unlock_entry; result = dax_pmd_load_hole(vma, pmd, &vmf, address, &iomap, &entry); break; @@ -1373,20 +1381,23 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address, break; } - finish_iomap: - if (ops->iomap_end) { - if (result == VM_FAULT_FALLBACK) { - ops->iomap_end(inode, pos, PMD_SIZE, 0, iomap_flags, - &iomap); - } else { - error = ops->iomap_end(inode, pos, PMD_SIZE, PMD_SIZE, - iomap_flags, &iomap); - if (error) - result = VM_FAULT_FALLBACK; - } - } unlock_entry: put_locked_mapping_entry(mapping, pgoff, entry); + finish_iomap: + if (ops->iomap_end) { + int copied = PMD_SIZE; + + if (result == VM_FAULT_FALLBACK) + copied = 0; + /* + * The fault is done by now and there's no way back (other + * thread may be already happily using PMD we have installed). + * Just ignore error from ->iomap_end since we cannot do much + * with it. + */ + ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags, + &iomap); + } fallback: if (result == VM_FAULT_FALLBACK) { split_huge_pmd(vma, pmd, address); From 1db175428ee374489448361213e9c3b749d14900 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 21 Oct 2016 11:33:49 +0200 Subject: [PATCH 6/6] ext4: Simplify DAX fault path Now that dax_iomap_fault() calls ->iomap_begin() without entry lock, we can use transaction starting in ext4_iomap_begin() and thus simplify ext4_dax_fault(). It also provides us proper retries in case of ENOSPC. Signed-off-by: Jan Kara Signed-off-by: Dan Williams --- fs/ext4/file.c | 48 ++++++++++-------------------------------------- 1 file changed, 10 insertions(+), 38 deletions(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index b5f184493c57..d663d3d7c81c 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -258,7 +258,6 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from) static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf) { int result; - handle_t *handle = NULL; struct inode *inode = file_inode(vma->vm_file); struct super_block *sb = inode->i_sb; bool write = vmf->flags & FAULT_FLAG_WRITE; @@ -266,24 +265,12 @@ static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf) if (write) { sb_start_pagefault(sb); file_update_time(vma->vm_file); - down_read(&EXT4_I(inode)->i_mmap_sem); - handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE, - EXT4_DATA_TRANS_BLOCKS(sb)); - } else - down_read(&EXT4_I(inode)->i_mmap_sem); - - if (IS_ERR(handle)) - result = VM_FAULT_SIGBUS; - else - result = dax_iomap_fault(vma, vmf, &ext4_iomap_ops); - - if (write) { - if (!IS_ERR(handle)) - ext4_journal_stop(handle); - up_read(&EXT4_I(inode)->i_mmap_sem); + } + down_read(&EXT4_I(inode)->i_mmap_sem); + result = dax_iomap_fault(vma, vmf, &ext4_iomap_ops); + up_read(&EXT4_I(inode)->i_mmap_sem); + if (write) sb_end_pagefault(sb); - } else - up_read(&EXT4_I(inode)->i_mmap_sem); return result; } @@ -292,7 +279,6 @@ static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, unsigned int flags) { int result; - handle_t *handle = NULL; struct inode *inode = file_inode(vma->vm_file); struct super_block *sb = inode->i_sb; bool write = flags & FAULT_FLAG_WRITE; @@ -300,27 +286,13 @@ static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr, if (write) { sb_start_pagefault(sb); file_update_time(vma->vm_file); - down_read(&EXT4_I(inode)->i_mmap_sem); - handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE, - ext4_chunk_trans_blocks(inode, - PMD_SIZE / PAGE_SIZE)); - } else - down_read(&EXT4_I(inode)->i_mmap_sem); - - if (IS_ERR(handle)) - result = VM_FAULT_SIGBUS; - else { - result = dax_iomap_pmd_fault(vma, addr, pmd, flags, - &ext4_iomap_ops); } - - if (write) { - if (!IS_ERR(handle)) - ext4_journal_stop(handle); - up_read(&EXT4_I(inode)->i_mmap_sem); + down_read(&EXT4_I(inode)->i_mmap_sem); + result = dax_iomap_pmd_fault(vma, addr, pmd, flags, + &ext4_iomap_ops); + up_read(&EXT4_I(inode)->i_mmap_sem); + if (write) sb_end_pagefault(sb); - } else - up_read(&EXT4_I(inode)->i_mmap_sem); return result; }