From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 28 Mar 2007 15:50:03 +0100 (BST) From: Hugh Dickins Subject: [PATCH 1/4] holepunch: fix shmem_truncate_range punching too far Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Miklos Szeredi , Badari Pulavarty , linux-mm@kvack.org List-ID: Miklos Szeredi observes BUG_ON(!entry) in shmem_writepage() triggered in rare circumstances, because shmem_truncate_range() erroneously removes partially truncated directory pages at the end of the range: later reclaim on pages pointing to these removed directories triggers the BUG. Indeed, and it can also cause data loss beyond the hole. Fix this as in the patch proposed by Miklos, but distinguish between "limit" (how far we need to search: ignore truncation's next_index optimization in the holepunch case - if there are races it's more consistent to act on the whole range specified) and "upper_limit" (how far we can free directory pages: generally we must be careful to keep partially punched pages, but can relax at end of file - i_size being held stable by i_mutex). Signed-off-by: Hugh Dickins Cc: Miklos Szeredi Cc: Badari Pulavarty --- Patch is against 2.6.21-rc5: intended for 2.6.21. To apply this series to -mm, please first revert Miklos' shmem-dont-release-lock-for-hole-punching.patch shmem-fix-bug-in-shmem_writepage.patch which these replace. mm/shmem.c | 32 +++++++++++++++++++++----------- 1 file changed, 21 insertions(+), 11 deletions(-) --- 2.6.21-rc5/mm/shmem.c 2007-03-07 13:09:01.000000000 +0000 +++ punch1/mm/shmem.c 2007-03-28 11:50:57.000000000 +0100 @@ -481,7 +481,8 @@ static void shmem_truncate_range(struct long nr_swaps_freed = 0; int offset; int freed; - int punch_hole = 0; + int punch_hole; + unsigned long upper_limit; inode->i_ctime = inode->i_mtime = CURRENT_TIME; idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; @@ -492,11 +493,18 @@ static void shmem_truncate_range(struct info->flags |= SHMEM_TRUNCATE; if (likely(end == (loff_t) -1)) { limit = info->next_index; + upper_limit = SHMEM_MAX_INDEX; info->next_index = idx; + punch_hole = 0; } else { - limit = (end + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; - if (limit > info->next_index) - limit = info->next_index; + if (end + 1 >= inode->i_size) { /* we may free a little more */ + limit = (inode->i_size + PAGE_CACHE_SIZE - 1) >> + PAGE_CACHE_SHIFT; + upper_limit = SHMEM_MAX_INDEX; + } else { + limit = (end + 1) >> PAGE_CACHE_SHIFT; + upper_limit = limit; + } punch_hole = 1; } @@ -520,10 +528,10 @@ static void shmem_truncate_range(struct * If there are no indirect blocks or we are punching a hole * below indirect blocks, nothing to be done. */ - if (!topdir || (punch_hole && (limit <= SHMEM_NR_DIRECT))) + if (!topdir || limit <= SHMEM_NR_DIRECT) goto done2; - BUG_ON(limit <= SHMEM_NR_DIRECT); + upper_limit -= SHMEM_NR_DIRECT; limit -= SHMEM_NR_DIRECT; idx = (idx > SHMEM_NR_DIRECT)? (idx - SHMEM_NR_DIRECT): 0; offset = idx % ENTRIES_PER_PAGE; @@ -543,7 +551,7 @@ static void shmem_truncate_range(struct if (*dir) { diroff = ((idx - ENTRIES_PER_PAGEPAGE/2) % ENTRIES_PER_PAGEPAGE) / ENTRIES_PER_PAGE; - if (!diroff && !offset) { + if (!diroff && !offset && upper_limit >= stage) { *dir = NULL; nr_pages_to_free++; list_add(&middir->lru, &pages_to_free); @@ -570,9 +578,11 @@ static void shmem_truncate_range(struct } stage = idx + ENTRIES_PER_PAGEPAGE; middir = *dir; - *dir = NULL; - nr_pages_to_free++; - list_add(&middir->lru, &pages_to_free); + if (upper_limit >= stage) { + *dir = NULL; + nr_pages_to_free++; + list_add(&middir->lru, &pages_to_free); + } shmem_dir_unmap(dir); cond_resched(); dir = shmem_dir_map(middir); @@ -598,7 +608,7 @@ static void shmem_truncate_range(struct } if (offset) offset = 0; - else if (subdir && !page_private(subdir)) { + else if (subdir && upper_limit - idx >= ENTRIES_PER_PAGE) { dir[diroff] = NULL; nr_pages_to_free++; list_add(&subdir->lru, &pages_to_free); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org