linux-kernel - Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with 6.0.0-rc3 through 6.0.0-rc7

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Date:   Wed, 19 Oct 2022 01:17:08 -0400
From:   Slade Watkins <srw@...dewatkins.net>
To:     Phillip Lougher <phillip@...ashfs.org.uk>
Cc:     bagasdotme@...il.com, hsinyi@...omium.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marc Miltenberger <marcmiltenberger@...il.com>,
        Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
        nicememory@...il.com,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        regressions@...ts.linux.dev
Subject: Re: BISECT result: 6.0.0-RC kernels trigger Firefox snap bug with
 6.0.0-rc3 through 6.0.0-rc7

Hi Phillip,

On Tue, Oct 18, 2022 at 1:42 PM Phillip Lougher <phillip@...ashfs.org.uk> wrote:
>
> This diff has fixed the problem with my repoducer.
> Please test and report your results.
>
> Phillip

Tested-by me just a few moments ago and can report this fixed the
problem. (I believe Mirsad also reported that this fixed it.)

Yours,
-srw

>
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index e56510964b22..e526eb7a1658 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -557,6 +557,7 @@ static void squashfs_readahead(struct readahead_control *ractl)
>                 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 readahead_control *ractl)
>
>                 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++) {
> diff --git a/fs/squashfs/page_actor.c b/fs/squashfs/page_actor.c
> index 54b93bf4a25c..6aa38f88e31c 100644
> --- a/fs/squashfs/page_actor.c
> +++ b/fs/squashfs/page_actor.c
> @@ -53,6 +53,7 @@ struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
>         actor->pages = pages;
>         actor->next_page = 0;
>         actor->tmp_buffer = NULL;
> +       actor->last_page = NULL;
>         actor->squashfs_first_page = cache_first_page;
>         actor->squashfs_next_page = cache_next_page;
>         actor->squashfs_finish_page = cache_finish_page;
> @@ -71,11 +72,13 @@ static void *handle_next_page(struct squashfs_page_actor *actor)
>                         (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++]);
>  }
>
> diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
> index 95ffbb543d91..97d4983559b1 100644
> --- a/fs/squashfs/page_actor.h
> +++ b/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 *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 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)
>  {