Merge tag 'hole_punch_for_v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs

Pull fs hole punching vs cache filling race fixes from Jan Kara:
 "Fix races leading to possible data corruption or stale data exposure
  in multiple filesystems when hole punching races with operations such
  as readahead.

  This is the series I was sending for the last merge window but with
  your objection fixed - now filemap_fault() has been modified to take
  invalidate_lock only when we need to create new page in the page cache
  and / or bring it uptodate"

* tag 'hole_punch_for_v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
  filesystems/locking: fix Malformed table warning
  cifs: Fix race between hole punch and page fault
  ceph: Fix race between hole punch and page fault
  fuse: Convert to using invalidate_lock
  f2fs: Convert to using invalidate_lock
  zonefs: Convert to using invalidate_lock
  xfs: Convert double locking of MMAPLOCK to use VFS helpers
  xfs: Convert to use invalidate_lock
  xfs: Refactor xfs_isilocked()
  ext2: Convert to using invalidate_lock
  ext4: Convert to use mapping->invalidate_lock
  mm: Add functions to lock invalidate_lock for two mappings
  mm: Protect operations adding pages to page cache with invalidate_lock
  documentation: Sync file_operations members with reality
  mm: Fix comments mentioning i_mutex

7 files changed, 162 insertions, 59 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index d1458ecf2f51..0fad08331cf4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -76,8 +76,9 @@
  *      ->swap_lock		(exclusive_swap_page, others)
  *        ->i_pages lock
  *
- *  ->i_mutex
- *    ->i_mmap_rwsem		(truncate->unmap_mapping_range)
+ *  ->i_rwsem
+ *    ->invalidate_lock		(acquired by fs in truncate path)
+ *      ->i_mmap_rwsem		(truncate->unmap_mapping_range)
  *
  *  ->mmap_lock
  *    ->i_mmap_rwsem
@@ -85,9 +86,10 @@
  *        ->i_pages lock	(arch-dependent flush_dcache_mmap_lock)
  *
  *  ->mmap_lock
- *    ->lock_page		(access_process_vm)
+ *    ->invalidate_lock		(filemap_fault)
+ *      ->lock_page		(filemap_fault, access_process_vm)
  *
- *  ->i_mutex			(generic_perform_write)
+ *  ->i_rwsem			(generic_perform_write)
  *    ->mmap_lock		(fault_in_pages_readable->do_page_fault)
  *
  *  bdi->wb.list_lock
@@ -1008,6 +1010,44 @@ EXPORT_SYMBOL(__page_cache_alloc);
 #endif
 
 /*
+ * filemap_invalidate_lock_two - lock invalidate_lock for two mappings
+ *
+ * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
+ *
+ * @mapping1: the first mapping to lock
+ * @mapping2: the second mapping to lock
+ */
+void filemap_invalidate_lock_two(struct address_space *mapping1,
+				 struct address_space *mapping2)
+{
+	if (mapping1 > mapping2)
+		swap(mapping1, mapping2);
+	if (mapping1)
+		down_write(&mapping1->invalidate_lock);
+	if (mapping2 && mapping1 != mapping2)
+		down_write_nested(&mapping2->invalidate_lock, 1);
+}
+EXPORT_SYMBOL(filemap_invalidate_lock_two);
+
+/*
+ * filemap_invalidate_unlock_two - unlock invalidate_lock for two mappings
+ *
+ * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
+ *
+ * @mapping1: the first mapping to unlock
+ * @mapping2: the second mapping to unlock
+ */
+void filemap_invalidate_unlock_two(struct address_space *mapping1,
+				   struct address_space *mapping2)
+{
+	if (mapping1)
+		up_write(&mapping1->invalidate_lock);
+	if (mapping2 && mapping1 != mapping2)
+		up_write(&mapping2->invalidate_lock);
+}
+EXPORT_SYMBOL(filemap_invalidate_unlock_two);
+
+/*
  * In order to wait for pages to become available there must be
  * waitqueues associated with pages. By using a hash table of
  * waitqueues where the bucket discipline is to maintain all
@@ -2368,20 +2408,30 @@ static int filemap_update_page(struct kiocb *iocb,
 {
 	int error;
 
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!filemap_invalidate_trylock_shared(mapping))
+			return -EAGAIN;
+	} else {
+		filemap_invalidate_lock_shared(mapping);
+	}
+
 	if (!trylock_page(page)) {
+		error = -EAGAIN;
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
-			return -EAGAIN;
+			goto unlock_mapping;
 		if (!(iocb->ki_flags & IOCB_WAITQ)) {
+			filemap_invalidate_unlock_shared(mapping);
 			put_and_wait_on_page_locked(page, TASK_KILLABLE);
 			return AOP_TRUNCATED_PAGE;
 		}
 		error = __lock_page_async(page, iocb->ki_waitq);
 		if (error)
-			return error;
+			goto unlock_mapping;
 	}
 
+	error = AOP_TRUNCATED_PAGE;
 	if (!page->mapping)
-		goto truncated;
+		goto unlock;
 
 	error = 0;
 	if (filemap_range_uptodate(mapping, iocb->ki_pos, iter, page))
@@ -2392,15 +2442,13 @@ static int filemap_update_page(struct kiocb *iocb,
 		goto unlock;
 
 	error = filemap_read_page(iocb->ki_filp, mapping, page);
-	if (error == AOP_TRUNCATED_PAGE)
-		put_page(page);
-	return error;
-truncated:
-	unlock_page(page);
-	put_page(page);
-	return AOP_TRUNCATED_PAGE;
+	goto unlock_mapping;
 unlock:
 	unlock_page(page);
+unlock_mapping:
+	filemap_invalidate_unlock_shared(mapping);
+	if (error == AOP_TRUNCATED_PAGE)
+		put_page(page);
 	return error;
 }
 
@@ -2415,6 +2463,19 @@ static int filemap_create_page(struct file *file,
 	if (!page)
 		return -ENOMEM;
 
+	/*
+	 * Protect against truncate / hole punch. Grabbing invalidate_lock here
+	 * assures we cannot instantiate and bring uptodate new pagecache pages
+	 * after evicting page cache during truncate and before actually
+	 * freeing blocks.  Note that we could release invalidate_lock after
+	 * inserting the page into page cache as the locked page would then be
+	 * enough to synchronize with hole punching. But there are code paths
+	 * such as filemap_update_page() filling in partially uptodate pages or
+	 * ->readpages() that need to hold invalidate_lock while mapping blocks
+	 * for IO so let's hold the lock here as well to keep locking rules
+	 * simple.
+	 */
+	filemap_invalidate_lock_shared(mapping);
 	error = add_to_page_cache_lru(page, mapping, index,
 			mapping_gfp_constraint(mapping, GFP_KERNEL));
 	if (error == -EEXIST)
@@ -2426,9 +2487,11 @@ static int filemap_create_page(struct file *file,
 	if (error)
 		goto error;
 
+	filemap_invalidate_unlock_shared(mapping);
 	pagevec_add(pvec, page);
 	return 0;
 error:
+	filemap_invalidate_unlock_shared(mapping);
 	put_page(page);
 	return error;
 }
@@ -2967,6 +3030,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	pgoff_t max_off;
 	struct page *page;
 	vm_fault_t ret = 0;
+	bool mapping_locked = false;
 
 	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 	if (unlikely(offset >= max_off))
@@ -2976,25 +3040,39 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	 * Do we have something in the page cache already?
 	 */
 	page = find_get_page(mapping, offset);
-	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
+	if (likely(page)) {
 		/*
-		 * We found the page, so try async readahead before
-		 * waiting for the lock.
+		 * We found the page, so try async readahead before waiting for
+		 * the lock.
 		 */
-		fpin = do_async_mmap_readahead(vmf, page);
-	} else if (!page) {
+		if (!(vmf->flags & FAULT_FLAG_TRIED))
+			fpin = do_async_mmap_readahead(vmf, page);
+		if (unlikely(!PageUptodate(page))) {
+			filemap_invalidate_lock_shared(mapping);
+			mapping_locked = true;
+		}
+	} else {
 		/* No page in the page cache at all */
 		count_vm_event(PGMAJFAULT);
 		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
 		ret = VM_FAULT_MAJOR;
 		fpin = do_sync_mmap_readahead(vmf);
 retry_find:
+		/*
+		 * See comment in filemap_create_page() why we need
+		 * invalidate_lock
+		 */
+		if (!mapping_locked) {
+			filemap_invalidate_lock_shared(mapping);
+			mapping_locked = true;
+		}
 		page = pagecache_get_page(mapping, offset,
 					  FGP_CREAT|FGP_FOR_MMAP,
 					  vmf->gfp_mask);
 		if (!page) {
 			if (fpin)
 				goto out_retry;
+			filemap_invalidate_unlock_shared(mapping);
 			return VM_FAULT_OOM;
 		}
 	}
@@ -3014,8 +3092,20 @@ retry_find:
 	 * We have a locked page in the page cache, now we need to check
 	 * that it's up-to-date. If not, it is going to be due to an error.
 	 */
-	if (unlikely(!PageUptodate(page)))
+	if (unlikely(!PageUptodate(page))) {
+		/*
+		 * The page was in cache and uptodate and now it is not.
+		 * Strange but possible since we didn't hold the page lock all
+		 * the time. Let's drop everything get the invalidate lock and
+		 * try again.
+		 */
+		if (!mapping_locked) {
+			unlock_page(page);
+			put_page(page);
+			goto retry_find;
+		}
 		goto page_not_uptodate;
+	}
 
 	/*
 	 * We've made it this far and we had to drop our mmap_lock, now is the
@@ -3026,6 +3116,8 @@ retry_find:
 		unlock_page(page);
 		goto out_retry;
 	}
+	if (mapping_locked)
+		filemap_invalidate_unlock_shared(mapping);
 
 	/*
 	 * Found the page and have a reference on it.
@@ -3056,6 +3148,7 @@ page_not_uptodate:
 
 	if (!error || error == AOP_TRUNCATED_PAGE)
 		goto retry_find;
+	filemap_invalidate_unlock_shared(mapping);
 
 	return VM_FAULT_SIGBUS;
 
@@ -3067,6 +3160,8 @@ out_retry:
 	 */
 	if (page)
 		put_page(page);
+	if (mapping_locked)
+		filemap_invalidate_unlock_shared(mapping);
 	if (fpin)
 		fput(fpin);
 	return ret | VM_FAULT_RETRY;
@@ -3437,6 +3532,8 @@ out:
  *
  * If the page does not get brought uptodate, return -EIO.
  *
+ * The function expects mapping->invalidate_lock to be already held.
+ *
  * Return: up to date page on success, ERR_PTR() on failure.
  */
 struct page *read_cache_page(struct address_space *mapping,
@@ -3460,6 +3557,8 @@ EXPORT_SYMBOL(read_cache_page);
  *
  * If the page does not get brought uptodate, return -EIO.
  *
+ * The function expects mapping->invalidate_lock to be already held.
+ *
  * Return: up to date page on success, ERR_PTR() on failure.
  */
 struct page *read_cache_page_gfp(struct address_space *mapping,
@@ -3704,12 +3803,12 @@ EXPORT_SYMBOL(generic_perform_write);
  * modification times and calls proper subroutines depending on whether we
  * do direct IO or a standard buffered write.
  *
- * It expects i_mutex to be grabbed unless we work on a block device or similar
+ * It expects i_rwsem to be grabbed unless we work on a block device or similar
  * object which does not need locking at all.
  *
  * This function does *not* take care of syncing data in case of O_SYNC write.
  * A caller has to handle it. This is mainly due to the fact that we want to
- * avoid syncing under i_mutex.
+ * avoid syncing under i_rwsem.
  *
  * Return:
  * * number of bytes written, even for truncated writes
@@ -3797,7 +3896,7 @@ EXPORT_SYMBOL(__generic_file_write_iter);
  *
  * This is a wrapper around __generic_file_write_iter() to be used by most
  * filesystems. It takes care of syncing the file in case of O_SYNC file
- * and acquires i_mutex as needed.
+ * and acquires i_rwsem as needed.
  * Return:
  * * negative error code if no data has been written at all of
  *   vfs_fsync_range() failed for a synchronous write
diff --git a/mm/madvise.c b/mm/madvise.c
index 5c065bc8b5f6..56324a3dbc4e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -912,7 +912,7 @@ static long madvise_remove(struct vm_area_struct *vma,
 			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 
 	/*
-	 * Filesystem's fallocate may need to take i_mutex.  We need to
+	 * Filesystem's fallocate may need to take i_rwsem.  We need to
 	 * explicitly grab a reference because the vma (and hence the
 	 * vma's reference to the file) can go away as soon as we drop
 	 * mmap_lock.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 470400cc7513..e1f87cf13235 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -866,7 +866,7 @@ static int me_pagecache_clean(struct page *p, unsigned long pfn)
 	/*
 	 * Truncation is a bit tricky. Enable it per file system for now.
 	 *
-	 * Open: to take i_mutex or not for this? Right now we don't.
+	 * Open: to take i_rwsem or not for this? Right now we don't.
 	 */
 	ret = truncate_error_page(p, pfn, mapping);
 out:
diff --git a/mm/readahead.c b/mm/readahead.c
index d589f147f4c2..41b75d76d36e 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -192,6 +192,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 	 */
 	unsigned int nofs = memalloc_nofs_save();
 
+	filemap_invalidate_lock_shared(mapping);
 	/*
 	 * Preallocate as many pages as we will need.
 	 */
@@ -236,6 +237,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 	 * will then handle the error.
 	 */
 	read_pages(ractl, &page_pool, false);
+	filemap_invalidate_unlock_shared(mapping);
 	memalloc_nofs_restore(nofs);
 }
 EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
diff --git a/mm/rmap.c b/mm/rmap.c
index b9eb5c12f3fe..2d29a57d29e8 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -20,28 +20,29 @@
 /*
  * Lock ordering in mm:
  *
- * inode->i_mutex	(while writing or truncating, not reading or faulting)
+ * inode->i_rwsem	(while writing or truncating, not reading or faulting)
  *   mm->mmap_lock
- *     page->flags PG_locked (lock_page)   * (see huegtlbfs below)
- *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
- *         mapping->i_mmap_rwsem
- *           hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
- *           anon_vma->rwsem
- *             mm->page_table_lock or pte_lock
- *               swap_lock (in swap_duplicate, swap_info_get)
- *                 mmlist_lock (in mmput, drain_mmlist and others)
- *                 mapping->private_lock (in __set_page_dirty_buffers)
- *                   lock_page_memcg move_lock (in __set_page_dirty_buffers)
- *                     i_pages lock (widely used)
- *                       lruvec->lru_lock (in lock_page_lruvec_irq)
- *                 inode->i_lock (in set_page_dirty's __mark_inode_dirty)
- *                 bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
- *                   sb_lock (within inode_lock in fs/fs-writeback.c)
- *                   i_pages lock (widely used, in set_page_dirty,
- *                             in arch-dependent flush_dcache_mmap_lock,
- *                             within bdi.wb->list_lock in __sync_single_inode)
+ *     mapping->invalidate_lock (in filemap_fault)
+ *       page->flags PG_locked (lock_page)   * (see hugetlbfs below)
+ *         hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
+ *           mapping->i_mmap_rwsem
+ *             hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
+ *             anon_vma->rwsem
+ *               mm->page_table_lock or pte_lock
+ *                 swap_lock (in swap_duplicate, swap_info_get)
+ *                   mmlist_lock (in mmput, drain_mmlist and others)
+ *                   mapping->private_lock (in __set_page_dirty_buffers)
+ *                     lock_page_memcg move_lock (in __set_page_dirty_buffers)
+ *                       i_pages lock (widely used)
+ *                         lruvec->lru_lock (in lock_page_lruvec_irq)
+ *                   inode->i_lock (in set_page_dirty's __mark_inode_dirty)
+ *                   bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
+ *                     sb_lock (within inode_lock in fs/fs-writeback.c)
+ *                     i_pages lock (widely used, in set_page_dirty,
+ *                               in arch-dependent flush_dcache_mmap_lock,
+ *                               within bdi.wb->list_lock in __sync_single_inode)
  *
- * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
+ * anon_vma->rwsem,mapping->i_mmap_rwsem   (memory_failure, collect_procs_anon)
  *   ->tasklist_lock
  *     pte map lock
  *
diff --git a/mm/shmem.c b/mm/shmem.c
index dacda7463d54..3107acee4f71 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -96,7 +96,7 @@ static struct vfsmount *shm_mnt;
 
 /*
  * shmem_fallocate communicates with shmem_fault or shmem_writepage via
- * inode->i_private (with i_mutex making sure that it has only one user at
+ * inode->i_private (with i_rwsem making sure that it has only one user at
  * a time): we would prefer not to enlarge the shmem inode just for that.
  */
 struct shmem_falloc {
@@ -774,7 +774,7 @@ static int shmem_free_swap(struct address_space *mapping,
  * Determine (in bytes) how many of the shmem object's pages mapped by the
  * given offsets are swapped out.
  *
- * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
+ * This is safe to call without i_rwsem or the i_pages lock thanks to RCU,
  * as long as the inode doesn't go away and racy results are not a problem.
  */
 unsigned long shmem_partial_swap_usage(struct address_space *mapping,
@@ -806,7 +806,7 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
  * Determine (in bytes) how many of the shmem object's pages mapped by the
  * given vma is swapped out.
  *
- * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
+ * This is safe to call without i_rwsem or the i_pages lock thanks to RCU,
  * as long as the inode doesn't go away and racy results are not a problem.
  */
 unsigned long shmem_swap_usage(struct vm_area_struct *vma)
@@ -1069,7 +1069,7 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
 		loff_t oldsize = inode->i_size;
 		loff_t newsize = attr->ia_size;
 
-		/* protected by i_mutex */
+		/* protected by i_rwsem */
 		if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
 		    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
 			return -EPERM;
@@ -2059,7 +2059,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
 	/*
 	 * Trinity finds that probing a hole which tmpfs is punching can
 	 * prevent the hole-punch from ever completing: which in turn
-	 * locks writers out with its hold on i_mutex.  So refrain from
+	 * locks writers out with its hold on i_rwsem.  So refrain from
 	 * faulting pages into the hole while it's being punched.  Although
 	 * shmem_undo_range() does remove the additions, it may be unable to
 	 * keep up, as each new page needs its own unmap_mapping_range() call,
@@ -2070,7 +2070,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
 	 * we just need to make racing faults a rare case.
 	 *
 	 * The implementation below would be much simpler if we just used a
-	 * standard mutex or completion: but we cannot take i_mutex in fault,
+	 * standard mutex or completion: but we cannot take i_rwsem in fault,
 	 * and bloating every shmem inode for this unlikely case would be sad.
 	 */
 	if (unlikely(inode->i_private)) {
@@ -2470,7 +2470,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	pgoff_t index = pos >> PAGE_SHIFT;
 
-	/* i_mutex is held by caller */
+	/* i_rwsem is held by caller */
 	if (unlikely(info->seals & (F_SEAL_GROW |
 				   F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
 		if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))
@@ -2570,7 +2570,7 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 		/*
 		 * We must evaluate after, since reads (unlike writes)
-		 * are called without i_mutex protection against truncate
+		 * are called without i_rwsem protection against truncate
 		 */
 		nr = PAGE_SIZE;
 		i_size = i_size_read(inode);
@@ -2640,7 +2640,7 @@ static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
 		return -ENXIO;
 
 	inode_lock(inode);
-	/* We're holding i_mutex so we can access i_size directly */
+	/* We're holding i_rwsem so we can access i_size directly */
 	offset = mapping_seek_hole_data(mapping, offset, inode->i_size, whence);
 	if (offset >= 0)
 		offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
@@ -2669,7 +2669,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 		loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
 		DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
 
-		/* protected by i_mutex */
+		/* protected by i_rwsem */
 		if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
 			error = -EPERM;
 			goto out;
diff --git a/mm/truncate.c b/mm/truncate.c
index 234ddd879caa..44ad5e515140 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -412,7 +412,8 @@ EXPORT_SYMBOL(truncate_inode_pages_range);
  * @mapping: mapping to truncate
  * @lstart: offset from which to truncate
  *
- * Called under (and serialised by) inode->i_mutex.
+ * Called under (and serialised by) inode->i_rwsem and
+ * mapping->invalidate_lock.
  *
  * Note: When this function returns, there can be a page in the process of
  * deletion (inside __delete_from_page_cache()) in the specified range.  Thus
@@ -429,7 +430,7 @@ EXPORT_SYMBOL(truncate_inode_pages);
  * truncate_inode_pages_final - truncate *all* pages before inode dies
  * @mapping: mapping to truncate
  *
- * Called under (and serialized by) inode->i_mutex.
+ * Called under (and serialized by) inode->i_rwsem.
  *
  * Filesystems have to use this in the .evict_inode path to inform the
  * VM that this is the final truncate and the inode is going away.
@@ -748,7 +749,7 @@ EXPORT_SYMBOL(truncate_pagecache);
  * setattr function when ATTR_SIZE is passed in.
  *
  * Must be called with a lock serializing truncates and writes (generally
- * i_mutex but e.g. xfs uses a different lock) and before all filesystem
+ * i_rwsem but e.g. xfs uses a different lock) and before all filesystem
  * specific block truncation has been performed.
  */
 void truncate_setsize(struct inode *inode, loff_t newsize)
@@ -777,7 +778,7 @@ EXPORT_SYMBOL(truncate_setsize);
  *
  * The function must be called after i_size is updated so that page fault
  * coming after we unlock the page will already see the new i_size.
- * The function must be called while we still hold i_mutex - this not only
+ * The function must be called while we still hold i_rwsem - this not only
  * makes sure i_size is stable but also that userspace cannot observe new
  * i_size value before we are prepared to store mmap writes at new inode size.
  */