The patch titled Subject: squashfs: fix read regression introduced in readahead code has been added to the -mm mm-hotfixes-unstable branch. Its filename is squashfs-fix-read-regression-introduced-in-readahead-code.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Phillip Lougher phillip@squashfs.org.uk Subject: squashfs: fix read regression introduced in readahead code Date: Thu, 20 Oct 2022 23:36:14 +0100
Patch series "squashfs: fix some regressions introduced in the readahead code".
This patchset fixes 3 regressions introduced by the recent readahead code changes. The first regression is causing "snaps" to randomly fail after a couple of hours or days, which how the regression came to light.
This patch (of 3):
If a file isn't a whole multiple of the page size, the last page will have trailing bytes unfilled.
There was a mistake in the readahead code which did this. In particular it incorrectly assumed that the last page in the readahead page array (page[nr_pages - 1]) will always contain the last page in the block, which if we're at file end, will be the page that needs to be zero filled.
But the readahead code may not return the last page in the block, which means it is unmapped and will be skipped by the decompressors (a temporary buffer used).
In this case the zero filling code will zero out the wrong page, leading to data corruption.
Fix this by by extending the "page actor" to return the last page if present, or NULL if a temporary buffer was used.
Link: https://lkml.kernel.org/r/20221020223616.7571-1-phillip@squashfs.org.uk Link: https://lkml.kernel.org/r/20221020223616.7571-2-phillip@squashfs.org.uk Fixes: 8fc78b6fe24c ("squashfs: implement readahead") Link: https://lore.kernel.org/lkml/b0c258c3-6dcf-aade-efc4-d62a8b3a1ce2@alu.unizg.... Signed-off-by: Phillip Lougher phillip@squashfs.org.uk Reported-by: Mirsad Goran Todorovac mirsad.todorovac@alu.unizg.hr Tested-by: Mirsad Goran Todorovac mirsad.todorovac@alu.unizg.hr Tested-by: Slade Watkins srw@sladewatkins.net Tested-by: Bagas Sanjaya bagasdotme@gmail.com Cc: stable@vger.kernel.org Cc: Dimitri John Ledkov dimitri.ledkov@canonical.com Cc: Hsin-Yi Wang hsinyi@chromium.org Cc: Thorsten Leemhuis regressions@leemhuis.info Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
fs/squashfs/file.c | 7 ++++--- fs/squashfs/page_actor.c | 3 +++ fs/squashfs/page_actor.h | 6 +++++- 3 files changed, 12 insertions(+), 4 deletions(-)
--- a/fs/squashfs/file.c~squashfs-fix-read-regression-introduced-in-readahead-code +++ a/fs/squashfs/file.c @@ -557,6 +557,7 @@ static void squashfs_readahead(struct re int res, bsize; u64 block = 0; unsigned int expected; + struct page *last_page;
nr_pages = __readahead_batch(ractl, pages, max_pages); if (!nr_pages) @@ -593,15 +594,15 @@ static void squashfs_readahead(struct re
res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
- squashfs_page_actor_free(actor); + last_page = squashfs_page_actor_free(actor);
if (res == expected) { int bytes;
/* Last page (if present) may have trailing bytes not filled */ bytes = res % PAGE_SIZE; - if (pages[nr_pages - 1]->index == file_end && bytes) - memzero_page(pages[nr_pages - 1], bytes, + if (index == file_end && bytes && last_page) + memzero_page(last_page, bytes, PAGE_SIZE - bytes);
for (i = 0; i < nr_pages; i++) { --- a/fs/squashfs/page_actor.c~squashfs-fix-read-regression-introduced-in-readahead-code +++ a/fs/squashfs/page_actor.c @@ -71,11 +71,13 @@ static void *handle_next_page(struct squ (actor->next_index != actor->page[actor->next_page]->index)) { actor->next_index++; actor->returned_pages++; + actor->last_page = NULL; return actor->alloc_buffer ? actor->tmp_buffer : ERR_PTR(-ENOMEM); }
actor->next_index++; actor->returned_pages++; + actor->last_page = actor->page[actor->next_page]; return actor->pageaddr = kmap_local_page(actor->page[actor->next_page++]); }
@@ -125,6 +127,7 @@ struct squashfs_page_actor *squashfs_pag actor->returned_pages = 0; actor->next_index = page[0]->index & ~((1 << (msblk->block_log - PAGE_SHIFT)) - 1); actor->pageaddr = NULL; + actor->last_page = NULL; actor->alloc_buffer = msblk->decompressor->alloc_buffer; actor->squashfs_first_page = direct_first_page; actor->squashfs_next_page = direct_next_page; --- a/fs/squashfs/page_actor.h~squashfs-fix-read-regression-introduced-in-readahead-code +++ a/fs/squashfs/page_actor.h @@ -16,6 +16,7 @@ struct squashfs_page_actor { void *(*squashfs_first_page)(struct squashfs_page_actor *); void *(*squashfs_next_page)(struct squashfs_page_actor *); void (*squashfs_finish_page)(struct squashfs_page_actor *); + struct page *last_page; int pages; int length; int next_page; @@ -29,10 +30,13 @@ extern struct squashfs_page_actor *squas extern struct squashfs_page_actor *squashfs_page_actor_init_special( struct squashfs_sb_info *msblk, struct page **page, int pages, int length); -static inline void squashfs_page_actor_free(struct squashfs_page_actor *actor) +static inline struct page *squashfs_page_actor_free(struct squashfs_page_actor *actor) { + struct page *last_page = actor->last_page; + kfree(actor->tmp_buffer); kfree(actor); + return last_page; } static inline void *squashfs_first_page(struct squashfs_page_actor *actor) { _
Patches currently in -mm which might be from phillip@squashfs.org.uk are
squashfs-fix-read-regression-introduced-in-readahead-code.patch squashfs-fix-extending-readahead-beyond-end-of-file.patch squashfs-fix-buffer-release-race-condition-in-readahead-code.patch