The patch titled
holepunch: fix shmem_truncate_range punching too far
has been removed from the -mm tree. Its filename was
holepunch-fix-shmem_truncate_range-punching-too-far.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
Subject: holepunch: fix shmem_truncate_range punching too far
From: Hugh Dickins <hugh@xxxxxxxxxxx>
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 <hugh@xxxxxxxxxxx>
Cc: Miklos Szeredi <mszeredi@xxxxxxx>
Cc: Badari Pulavarty <pbadari@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)
diff -puN mm/shmem.c~holepunch-fix-shmem_truncate_range-punching-too-far mm/shmem.c
--- a/mm/shmem.c~holepunch-fix-shmem_truncate_range-punching-too-far
+++ a/mm/shmem.c
@@ -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);
_
Patches currently in -mm which might be from hugh@xxxxxxxxxxx are
origin.patch
git-drm.patch
mm-more-rmap-checking.patch
mm-make-read_cache_page-synchronous.patch
fs-buffer-dont-pageuptodate-without-page-locked.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated.patch
i386-add-ptep_test_and_clear_dirtyyoung.patch
i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung.patch
i386-use-pte_update_defer-in-ptep_test_and_clear_dirtyyoung-fix.patch
smaps-extract-pmd-walker-from-smaps-code.patch
smaps-add-pages-referenced-count-to-smaps.patch
smaps-add-clear_refs-file-to-clear-reference.patch
smaps-add-clear_refs-file-to-clear-reference-fix.patch
smaps-add-clear_refs-file-to-clear-reference-fix-fix-2.patch
smaps-use-ptep_test_and_clear_young.patch
tty-in-tiocsctty-when-we-steal-a-tty-hang-it-up-fix.patch
ext2-reservations.patch
ext2-balloc-use-io_error-label.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated-swap-prefetch.patch
-
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