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Message-ID: <d2580643-f58e-c1b0-7671-c5bbb38c05d0@alu.unizg.hr>
Date: Thu, 20 Oct 2022 18:00:06 +0200
From: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
To: Jintao Yin <nicememory@...il.com>, phillip@...ashfs.org.uk
Cc: bagasdotme@...il.com, hsinyi@...omium.org,
linux-kernel@...r.kernel.org, marcmiltenberger@...il.com,
regressions@...mhuis.info, regressions@...ts.linux.dev,
srw@...dewatkins.net
Subject: Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with
6.0.0-rc3 through 6.0.0-rc7
On 10/20/22 15:55, Jintao Yin wrote:
> Hi all,
>
> After review the details of page actor, the tail bytes may be written to
> a temp buffer instead the last used page. So before diff would wrongly
> memzero a page which is not the tail bytes in.
>
> In this diff fixes it by caculation of the real index the trailing bytes
> in and check if the last used page matches this index. If the page is
> the real tail bytes in, then memzero the trailing bypte of the page.
>
> Please help test and any feedbacks are welcome.
>
> Thanks,
>
> Jintao
Hi, Jintao,
I have very good news. The bug reproducing Firefox windows and tabs
setup that
crashed with core dump in your previous diff now works a OK.
The build from the previous email was v6.0.2+ and this one is 6.1-rc1+.
As a newbie I cannot say anything of importance, but I feel good about this
being done.
Have a nice day!
Mirsad
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index e56510964b22..e1fafd10a850 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -506,8 +506,9 @@ static int squashfs_readahead_fragment(struct page **page,
> squashfs_i(inode)->fragment_size);
> struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
> unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
> + int res = buffer->error;
>
> - if (buffer->error)
> + if (res)
> goto out;
>
> expected += squashfs_i(inode)->fragment_offset;
> @@ -529,7 +530,7 @@ static int squashfs_readahead_fragment(struct page **page,
>
> out:
> squashfs_cache_put(buffer);
> - return buffer->error;
> + return res;
> }
>
> static void squashfs_readahead(struct readahead_control *ractl)
> @@ -557,6 +558,7 @@ static void squashfs_readahead(struct readahead_control *ractl)
> int res, bsize;
> u64 block = 0;
> unsigned int expected;
> + int nr_used_pages;
>
> nr_pages = __readahead_batch(ractl, pages, max_pages);
> if (!nr_pages)
> @@ -593,18 +595,21 @@ static void squashfs_readahead(struct readahead_control *ractl)
>
> res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
>
> - squashfs_page_actor_free(actor);
> + nr_used_pages = squashfs_page_actor_free(actor);
>
> if (res == expected) {
> int bytes;
> + pgoff_t bytes_index;
>
> /* 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,
> + bytes_index = (index << shift) + ((res - bytes) >> PAGE_SHIFT);
> + if (bytes && nr_used_pages > 0 &&
> + pages[nr_used_pages - 1]->index == bytes_index)
> + memzero_page(pages[nr_used_pages - 1], bytes,
> PAGE_SIZE - bytes);
>
> - for (i = 0; i < nr_pages; i++) {
> + for (i = 0; i < nr_used_pages; i++) {
> flush_dcache_page(pages[i]);
> SetPageUptodate(pages[i]);
> }
> diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
> index f1ccad519e28..ee462ef380bf 100644
> --- a/fs/squashfs/file_direct.c
> +++ b/fs/squashfs/file_direct.c
> @@ -26,14 +26,14 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
> struct inode *inode = target_page->mapping->host;
> struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
>
> - int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
> - int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
> - int start_index = target_page->index & ~mask;
> - int end_index = start_index | mask;
> - int i, n, pages, bytes, res = -ENOMEM;
> + pgoff_t file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
> + pgoff_t mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
> + pgoff_t start_index = target_page->index & ~mask;
> + pgoff_t end_index = start_index | mask;
> + int i, pages, used_pages, bytes, res = -ENOMEM;
> + pgoff_t n, bytes_index;
> struct page **page;
> struct squashfs_page_actor *actor;
> - void *pageaddr;
>
> if (end_index > file_end)
> end_index = file_end;
> @@ -74,7 +74,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
> /* Decompress directly into the page cache buffers */
> res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
>
> - squashfs_page_actor_free(actor);
> + used_pages = squashfs_page_actor_free(actor);
>
> if (res < 0)
> goto mark_errored;
> @@ -86,16 +86,19 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
>
> /* Last page (if present) may have trailing bytes not filled */
> bytes = res % PAGE_SIZE;
> - if (page[pages - 1]->index == end_index && bytes) {
> - pageaddr = kmap_local_page(page[pages - 1]);
> - memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
> - kunmap_local(pageaddr);
> + bytes_index = start_index + ((res - bytes) >> PAGE_SHIFT);
> + if (used_pages > 0 && bytes &&
> + page[used_pages - 1]->index == bytes_index) {
> + memzero_page(page[used_pages - 1], bytes,
> + PAGE_SIZE - bytes);
> }
>
> /* Mark pages as uptodate, unlock and release */
> for (i = 0; i < pages; i++) {
> - flush_dcache_page(page[i]);
> - SetPageUptodate(page[i]);
> + if (i < used_pages) {
> + flush_dcache_page(page[i]);
> + SetPageUptodate(page[i]);
> + }
> unlock_page(page[i]);
> if (page[i] != target_page)
> put_page(page[i]);
> @@ -112,8 +115,10 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
> for (i = 0; i < pages; i++) {
> if (page[i] == NULL || page[i] == target_page)
> continue;
> - flush_dcache_page(page[i]);
> - SetPageError(page[i]);
> + if (i < used_pages) {
> + flush_dcache_page(page[i]);
> + SetPageError(page[i]);
> + }
> unlock_page(page[i]);
> put_page(page[i]);
> }
> diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
> index 95ffbb543d91..c2c5c3937ef9 100644
> --- a/fs/squashfs/page_actor.h
> +++ b/fs/squashfs/page_actor.h
> @@ -29,10 +29,12 @@ extern struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
> 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 int squashfs_page_actor_free(struct squashfs_page_actor *actor)
> {
> + int res = actor->next_page;
> kfree(actor->tmp_buffer);
> kfree(actor);
> + return res;
> }
> static inline void *squashfs_first_page(struct squashfs_page_actor *actor)
> {
--
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
--
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
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