In __dax_pmd_fault() we currently assume that get_block() will always set bh.b_bdev and we unconditionally dereference it in __dax_dbg(). This assumption isn't always true - when called for reads of holes ext4_dax_mmap_get_block() returns a buffer head where bh->b_bdev is never set. I hit this BUG while testing the DAX PMD fault path. Instead, initialize bh.b_bdev before passing bh into get_block(). It is possible that the filesystem's get_block() will update bh.b_bdev, and this is fine - we just want to initialize bh.b_bdev to something reasonable so that the calls to __dax_dbg() work and print something useful. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Cc: Dan Williams <dan.j.williams(a)intel.com&gt; --- fs/dax.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/dax.c b/fs/dax.c index 7af8797..513bba5 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -624,6 +624,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, } memset(&bh, 0, sizeof(bh)); + bh.b_bdev = inode->i_sb->s_bdev; block = (sector_t)pgoff << (PAGE_SHIFT - blkbits); bh.b_size = PMD_SIZE; -- 2.5.0

On Tue, Jan 12, 2016 at 10:34:58AM +0100, Jan Kara wrote: I don't think we need it anywhere else. The only reason that we need to initialize the bh.b_bdev manually in the __dax_pmd_fault() path is that if the get_block() call ends up finding a hole (so doesn't fill out b_bdev) we still go through the dax_pmd_dbg() path to print an error message, which uses b_bdev. I believe that in the other paths where we hit a hole, such as __dax_fault(), we don't use b_bdev because we don't have the same error path prints, and the regular code for handling holes doesn't use b_bdev. That being said, if you feel like it's cleaner to initialize it everywhere so everything is consistent and we don't have to worry about it, I'm fine to make the change.

When we get a DAX PMD fault for a write it is possible that there could be some number of 4k zero pages already present for the same range that were inserted to service reads from a hole. These 4k zero pages need to be unmapped from the VMAs and removed from the struct address_space radix tree before the real DAX PMD entry can be inserted. For PTE faults this same use case also exists and is handled by a combination of unmap_mapping_range() to unmap the VMAs and delete_from_page_cache() to remove the page from the address_space radix tree. For PMD faults we do have a call to unmap_mapping_range() (protected by a buffer_new() check), but nothing clears out the radix tree entry. The buffer_new() check is also incorrect as the current ext4 and XFS filesystem code will never return a buffer_head with BH_New set, even when allocating new blocks over a hole. Instead the filesystem will zero the blocks manually and return a buffer_head with only BH_Mapped set. Fix this situation by removing the buffer_new() check and adding a call to truncate_inode_pages_range() to clear out the radix tree entries before we insert the DAX PMD. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reported-by: Dan Williams <dan.j.williams(a)intel.com&gt; Tested-by: Dan Williams <dan.j.williams(a)intel.com&gt; --- fs/dax.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 513bba5..5b84a46 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -589,6 +589,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, bool write = flags & FAULT_FLAG_WRITE; struct block_device *bdev; pgoff_t size, pgoff; + loff_t lstart, lend; sector_t block; int result = 0; @@ -643,15 +644,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, goto fallback; } - /* - * If we allocated new storage, make sure no process has any - * zero pages covering this hole - */ - if (buffer_new(&bh)) { - i_mmap_unlock_read(mapping); - unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0); - i_mmap_lock_read(mapping); - } + /* make sure no process has any zero pages covering this hole */ + lstart = pgoff << PAGE_SHIFT; + lend = lstart + PMD_SIZE - 1; /* inclusive */ + i_mmap_unlock_read(mapping); + unmap_mapping_range(mapping, lstart, PMD_SIZE, 0); + truncate_inode_pages_range(mapping, lstart, lend); + i_mmap_lock_read(mapping); /* * If a truncate happened while we were allocating blocks, we may @@ -665,7 +664,8 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, goto out; } if ((pgoff | PG_PMD_COLOUR) >= size) { - dax_pmd_dbg(&bh, address, "pgoff unaligned"); + dax_pmd_dbg(&bh, address, + "offset + huge page size > file size"); goto fallback; } -- 2.5.0

On Tue, Jan 12, 2016 at 10:44:51AM +0100, Jan Kara wrote: Cool, thank you for the review! I think we can probably just take it when we're done with the truncate() - I'll fix for v9. Nice. I'll change it for v9.

Add support for tracking dirty DAX entries in the struct address_space radix tree. This tree is already used for dirty page writeback, and it already supports the use of exceptional (non struct page*) entries. In order to properly track dirty DAX pages we will insert new exceptional entries into the radix tree that represent dirty DAX PTE or PMD pages. These exceptional entries will also contain the writeback sectors for the PTE or PMD faults that we can use at fsync/msync time. There are currently two types of exceptional entries (shmem and shadow) that can be placed into the radix tree, and this adds a third. We rely on the fact that only one type of exceptional entry can be found in a given radix tree based on its usage. This happens for free with DAX vs shmem but we explicitly prevent shadow entries from being added to radix trees for DAX mappings. The only shadow entries that would be generated for DAX radix trees would be to track zero page mappings that were created for holes. These pages would receive minimal benefit from having shadow entries, and the choice to have only one type of exceptional entry in a given radix tree makes the logic simpler both in clear_exceptional_entry() and in the rest of DAX. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reviewed-by: Jan Kara <jack(a)suse.cz&gt; --- fs/block_dev.c | 2 +- fs/inode.c | 2 +- include/linux/dax.h | 5 ++++ include/linux/fs.h | 3 +- include/linux/radix-tree.h | 9 ++++++ mm/filemap.c | 17 ++++++++---- mm/truncate.c | 69 ++++++++++++++++++++++++++-------------------- mm/vmscan.c | 9 +++++- mm/workingset.c | 4 +-- 9 files changed, 78 insertions(+), 42 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index e123641..303b7cd 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -75,7 +75,7 @@ void kill_bdev(struct block_device *bdev) { struct address_space *mapping = bdev->bd_inode->i_mapping; - if (mapping->nrpages == 0 && mapping->nrshadows == 0) + if (mapping->nrpages == 0 && mapping->nrexceptional == 0) return; invalidate_bh_lrus(); diff --git a/fs/inode.c b/fs/inode.c index 4c8f719..6e3e5d0 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -495,7 +495,7 @@ void clear_inode(struct inode *inode) */ spin_lock_irq(&inode->i_data.tree_lock); BUG_ON(inode->i_data.nrpages); - BUG_ON(inode->i_data.nrshadows); + BUG_ON(inode->i_data.nrexceptional); spin_unlock_irq(&inode->i_data.tree_lock); BUG_ON(!list_empty(&inode->i_data.private_list)); BUG_ON(!(inode->i_state & I_FREEING)); diff --git a/include/linux/dax.h b/include/linux/dax.h index b415e52..e9d57f68 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma) { return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host); } + +static inline bool dax_mapping(struct address_space *mapping) +{ + return mapping->host && IS_DAX(mapping->host); +} #endif diff --git a/include/linux/fs.h b/include/linux/fs.h index ddb7bad..fdab768 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -433,7 +433,8 @@ struct address_space { struct rw_semaphore i_mmap_rwsem; /* protect tree, count, list */ /* Protected by tree_lock together with the radix tree */ unsigned long nrpages; /* number of total pages */ - unsigned long nrshadows; /* number of shadow entries */ + /* number of shadow or DAX exceptional entries */ + unsigned long nrexceptional; pgoff_t writeback_index;/* writeback starts here */ const struct address_space_operations *a_ops; /* methods */ unsigned long flags; /* error bits/gfp mask */ diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index 57e7d87..7c88ad1 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -51,6 +51,15 @@ #define RADIX_TREE_EXCEPTIONAL_ENTRY 2 #define RADIX_TREE_EXCEPTIONAL_SHIFT 2 +#define RADIX_DAX_MASK 0xf +#define RADIX_DAX_SHIFT 4 +#define RADIX_DAX_PTE (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY) +#define RADIX_DAX_PMD (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY) +#define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_MASK) +#define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT)) +#define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \ + RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE))) + static inline int radix_tree_is_indirect_ptr(void *ptr) { return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR); diff --git a/mm/filemap.c b/mm/filemap.c index 847ee43..7b8be78 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -11,6 +11,7 @@ */ #include <linux/export.h> #include <linux/compiler.h> +#include <linux/dax.h> #include <linux/fs.h> #include <linux/uaccess.h> #include <linux/capability.h> @@ -123,9 +124,9 @@ static void page_cache_tree_delete(struct address_space *mapping, __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot); if (shadow) { - mapping->nrshadows++; + mapping->nrexceptional++; /* - * Make sure the nrshadows update is committed before + * Make sure the nrexceptional update is committed before * the nrpages update so that final truncate racing * with reclaim does not see both counters 0 at the * same time and miss a shadow entry. @@ -579,9 +580,13 @@ static int page_cache_tree_insert(struct address_space *mapping, p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock); if (!radix_tree_exceptional_entry(p)) return -EEXIST; + + if (WARN_ON(dax_mapping(mapping))) + return -EINVAL; + if (shadowp) *shadowp = p; - mapping->nrshadows--; + mapping->nrexceptional--; if (node) workingset_node_shadows_dec(node); } @@ -1245,9 +1250,9 @@ repeat: if (radix_tree_deref_retry(page)) goto restart; /* - * A shadow entry of a recently evicted page, - * or a swap entry from shmem/tmpfs. Return - * it without attempting to raise page count. + * A shadow entry of a recently evicted page, a swap + * entry from shmem/tmpfs or a DAX entry. Return it + * without attempting to raise page count. */ goto export; } diff --git a/mm/truncate.c b/mm/truncate.c index 76e35ad..e3ee0e2 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -9,6 +9,7 @@ #include <linux/kernel.h> #include <linux/backing-dev.h> +#include <linux/dax.h> #include <linux/gfp.h> #include <linux/mm.h> #include <linux/swap.h> @@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping, return; spin_lock_irq(&mapping->tree_lock); - /* - * Regular page slots are stabilized by the page lock even - * without the tree itself locked. These unlocked entries - * need verification under the tree lock. - */ - if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot)) - goto unlock; - if (*slot != entry) - goto unlock; - radix_tree_replace_slot(slot, NULL); - mapping->nrshadows--; - if (!node) - goto unlock; - workingset_node_shadows_dec(node); - /* - * Don't track node without shadow entries. - * - * Avoid acquiring the list_lru lock if already untracked. - * The list_empty() test is safe as node->private_list is - * protected by mapping->tree_lock. - */ - if (!workingset_node_shadows(node) && - !list_empty(&node->private_list)) - list_lru_del(&workingset_shadow_nodes, &node->private_list); - __radix_tree_delete_node(&mapping->page_tree, node); + + if (dax_mapping(mapping)) { + if (radix_tree_delete_item(&mapping->page_tree, index, entry)) + mapping->nrexceptional--; + } else { + /* + * Regular page slots are stabilized by the page lock even + * without the tree itself locked. These unlocked entries + * need verification under the tree lock. + */ + if (!__radix_tree_lookup(&mapping->page_tree, index, &node, + &slot)) + goto unlock; + if (*slot != entry) + goto unlock; + radix_tree_replace_slot(slot, NULL); + mapping->nrexceptional--; + if (!node) + goto unlock; + workingset_node_shadows_dec(node); + /* + * Don't track node without shadow entries. + * + * Avoid acquiring the list_lru lock if already untracked. + * The list_empty() test is safe as node->private_list is + * protected by mapping->tree_lock. + */ + if (!workingset_node_shadows(node) && + !list_empty(&node->private_list)) + list_lru_del(&workingset_shadow_nodes, + &node->private_list); + __radix_tree_delete_node(&mapping->page_tree, node); + } unlock: spin_unlock_irq(&mapping->tree_lock); } @@ -228,7 +237,7 @@ void truncate_inode_pages_range(struct address_space *mapping, int i; cleancache_invalidate_inode(mapping); - if (mapping->nrpages == 0 && mapping->nrshadows == 0) + if (mapping->nrpages == 0 && mapping->nrexceptional == 0) return; /* Offsets within partial pages */ @@ -402,7 +411,7 @@ EXPORT_SYMBOL(truncate_inode_pages); */ void truncate_inode_pages_final(struct address_space *mapping) { - unsigned long nrshadows; + unsigned long nrexceptional; unsigned long nrpages; /* @@ -416,14 +425,14 @@ void truncate_inode_pages_final(struct address_space *mapping) /* * When reclaim installs eviction entries, it increases - * nrshadows first, then decreases nrpages. Make sure we see + * nrexceptional first, then decreases nrpages. Make sure we see * this in the right order or we might miss an entry. */ nrpages = mapping->nrpages; smp_rmb(); - nrshadows = mapping->nrshadows; + nrexceptional = mapping->nrexceptional; - if (nrpages || nrshadows) { + if (nrpages || nrexceptional) { /* * As truncation uses a lockless tree lookup, cycle * the tree lock to make sure any ongoing tree diff --git a/mm/vmscan.c b/mm/vmscan.c index 44ec50f..30e0cd7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -46,6 +46,7 @@ #include <linux/oom.h> #include <linux/prefetch.h> #include <linux/printk.h> +#include <linux/dax.h> #include <asm/tlbflush.h> #include <asm/div64.h> @@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, * inode reclaim needs to empty out the radix tree or * the nodes are lost. Don't plant shadows behind its * back. + * + * We also don't store shadows for DAX mappings because the + * only page cache pages found in these are zero pages + * covering holes, and because we don't want to mix DAX + * exceptional entries and shadow exceptional entries in the + * same page_tree. */ if (reclaimed && page_is_file_cache(page) && - !mapping_exiting(mapping)) + !mapping_exiting(mapping) && !dax_mapping(mapping)) shadow = workingset_eviction(mapping, page); __delete_from_page_cache(page, shadow, memcg); spin_unlock_irqrestore(&mapping->tree_lock, flags); diff --git a/mm/workingset.c b/mm/workingset.c index aa01713..61ead9e 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -351,8 +351,8 @@ static enum lru_status shadow_lru_isolate(struct list_head *item, node->slots[i] = NULL; BUG_ON(node->count < (1U << RADIX_TREE_COUNT_SHIFT)); node->count -= 1U << RADIX_TREE_COUNT_SHIFT; - BUG_ON(!mapping->nrshadows); - mapping->nrshadows--; + BUG_ON(!mapping->nrexceptional); + mapping->nrexceptional--; } } BUG_ON(node->count); -- 2.5.0

On Wed, Jan 13, 2016 at 10:44:11AM +0100, Jan Kara wrote: I think (and will verify) that the DAX code just unmaps the entire PMD range when we receive a hole punch request inside of the PMD. If this is true then I think the radix tree code should behave the same way and just remove the PMD entry in the radix tree. This will cause new accesses that used to land in the PMD range to get new page faults. These faults will call get_blocks(), where presumably the filesystem will tell us that we don't have a contiguous 2MiB range anymore, so we will fall back to PTE faults. These PTEs will fill in both the radix tree and the page tables. So, I think the work here is to verify the behavior of DAX wrt hole punches for PMD ranges, and make the radix tree code match that behavior. Sound good?

On Fri, Jan 15, 2016 at 02:22:49PM +0100, Jan Kara wrote: Yep, agreed.

Add find_get_entries_tag() to the family of functions that include find_get_entries(), find_get_pages() and find_get_pages_tag(). This is needed for DAX dirty page handling because we need a list of both page offsets and radix tree entries ('indices' and 'entries' in this function) that are marked with the PAGECACHE_TAG_TOWRITE tag. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reviewed-by: Jan Kara <jack(a)suse.cz&gt; --- include/linux/pagemap.h | 3 +++ mm/filemap.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 4d08b6c..92395a0 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -361,6 +361,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start, unsigned int nr_pages, struct page **pages); unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index, int tag, unsigned int nr_pages, struct page **pages); +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start, + int tag, unsigned int nr_entries, + struct page **entries, pgoff_t *indices); struct page *grab_cache_page_write_begin(struct address_space *mapping, pgoff_t index, unsigned flags); diff --git a/mm/filemap.c b/mm/filemap.c index 7b8be78..1e215fc 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1499,6 +1499,74 @@ repeat: } EXPORT_SYMBOL(find_get_pages_tag); +/** + * find_get_entries_tag - find and return entries that match @tag + * @mapping: the address_space to search + * @start: the starting page cache index + * @tag: the tag index + * @nr_entries: the maximum number of entries + * @entries: where the resulting entries are placed + * @indices: the cache indices corresponding to the entries in @entries + * + * Like find_get_entries, except we only return entries which are tagged with + * @tag. + */ +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start, + int tag, unsigned int nr_entries, + struct page **entries, pgoff_t *indices) +{ + void **slot; + unsigned int ret = 0; + struct radix_tree_iter iter; + + if (!nr_entries) + return 0; + + rcu_read_lock(); +restart: + radix_tree_for_each_tagged(slot, &mapping->page_tree, + &iter, start, tag) { + struct page *page; +repeat: + page = radix_tree_deref_slot(slot); + if (unlikely(!page)) + continue; + if (radix_tree_exception(page)) { + if (radix_tree_deref_retry(page)) { + /* + * Transient condition which can only trigger + * when entry at index 0 moves out of or back + * to root: none yet gotten, safe to restart. + */ + goto restart; + } + + /* + * A shadow entry of a recently evicted page, a swap + * entry from shmem/tmpfs or a DAX entry. Return it + * without attempting to raise page count. + */ + goto export; + } + if (!page_cache_get_speculative(page)) + goto repeat; + + /* Has the page moved? */ + if (unlikely(page != *slot)) { + page_cache_release(page); + goto repeat; + } +export: + indices[ret] = iter.index; + entries[ret] = page; + if (++ret == nr_entries) + break; + } + rcu_read_unlock(); + return ret; +} +EXPORT_SYMBOL(find_get_entries_tag); + /* * CD/DVDs are error prone. When a medium error occurs, the driver may fail * a _large_ part of the i/o request. Imagine the worst scenario: -- 2.5.0

On Thu 07-01-16 22:27:56, Ross Zwisler wrote: Some comments below. In theory, you can delete here DIRTY / TOWRITE PTE entry and insert a clean PMD entry instead of it. That will cause fsync() to miss some flushes. So you should make sure you transfer all the tags to the new entry. This seems to be somewhat racy as well - if there are two fsyncs running against the same inode, one wins the race and clears TOWRITE tag, the second then bails out and may finish before the skipped page gets flushed. So we should clear the TOWRITE tag only after the range is flushed. This can result in some amount of duplicit flushing but I don't think the race will happen that frequently in practice to be performance relevant. And secondly: You must write-protect all mappings of the flushed range so that you get fault when the sector gets written-to again. We spoke about this in the past already but somehow it got lost and I forgot about it as well. You need something like rmap_walk_file()... ... Why is NO_SECTOR argument correct here? Honza -- Jan Kara <jack(a)suse.com&gt; SUSE Labs, CR

On Wed 13-01-16 00:30:19, Ross Zwisler wrote: Ahaa! Somehow I imagined tag_pages_for_writeback() clears DIRTY radix tree tags but it does not (I should have known, I have written that functions few years ago ;). Makes sense. Thanks for clarification. So the explanation of this should be somewhere so that everyone knows that we must have radix tree entries even for clean mapped blocks. Because upto know that was not clear to me. Also __dax_pmd_fault() seems to insert entries only for write fault so the assumption doesn't seem to hold there? I'm somewhat uneasy that a bug in this logic can be hidden as a simple race with hole punching. But I guess I can live with that. Honza -- Jan Kara <jack(a)suse.com&gt; SUSE Labs, CR

On Wed 13-01-16 11:58:02, Ross Zwisler wrote: Ouch, I wasn't aware of this asymetry between PMD and PTE faults. OK, so please just document this all somewhere because I'm pretty sure casual reader won't be able to figure this all out just from the code. Honza -- Jan Kara <jack(a)suse.com&gt; SUSE Labs, CR

To properly support the new DAX fsync/msync infrastructure filesystems need to call dax_pfn_mkwrite() so that DAX can track when user pages are dirtied. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reviewed-by: Jan Kara <jack(a)suse.cz&gt; --- fs/ext4/file.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 60683ab..fa899c9 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma, { struct inode *inode = file_inode(vma->vm_file); struct super_block *sb = inode->i_sb; - int ret = VM_FAULT_NOPAGE; loff_t size; + int ret; sb_start_pagefault(sb); file_update_time(vma->vm_file); @@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma, size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; if (vmf->pgoff >= size) ret = VM_FAULT_SIGBUS; + else + ret = dax_pfn_mkwrite(vma, vmf); up_read(&EXT4_I(inode)->i_mmap_sem); sb_end_pagefault(sb); -- 2.5.0