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From:   Ming Lei <tom.leiming@gmail.com>
Date:   Wed, 9 Sep 2020 11:36:15 +0800
Message-ID: <CACVXFVMPHhA9_Pk-KGROimwxJBM_5SHmjH+CKkkNLJWGk2gmFw@mail.gmail.com>
Subject: Re: [RESEND PATCH 1/1] block: Set same_page to false in
 __bio_try_merge_page if ret is false
To:     Ritesh Harjani <riteshh@linux.ibm.com>
Cc:     linux-block <linux-block@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        "open list:XFS FILESYSTEM" <linux-xfs@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Shivaprasad G Bhat <sbhat@linux.ibm.com>,
        Anju T Sudhakar <anju@linux.vnet.ibm.com>
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On Wed, Sep 9, 2020 at 11:16 AM Ritesh Harjani <riteshh@linux.ibm.com> wrote:
>
> If we hit the UINT_MAX limit of bio->bi_iter.bi_size and so we are anyway
> not merging this page in this bio, then it make sense to make same_page
> also as false before returning.
>
> Without this patch, we hit below WARNING in iomap.
> This mostly happens with very large memory system and / or after tweaking
> vm dirty threshold params to delay writeback of dirty data.
>
> WARNING: CPU: 18 PID: 5130 at fs/iomap/buffered-io.c:74 iomap_page_release+0x120/0x150
>  CPU: 18 PID: 5130 Comm: fio Kdump: loaded Tainted: G        W         5.8.0-rc3 #6
>  Call Trace:
>   __remove_mapping+0x154/0x320 (unreliable)
>   iomap_releasepage+0x80/0x180
>   try_to_release_page+0x94/0xe0
>   invalidate_inode_page+0xc8/0x110
>   invalidate_mapping_pages+0x1dc/0x540
>   generic_fadvise+0x3c8/0x450
>   xfs_file_fadvise+0x2c/0xe0 [xfs]
>   vfs_fadvise+0x3c/0x60
>   ksys_fadvise64_64+0x68/0xe0
>   sys_fadvise64+0x28/0x40
>   system_call_exception+0xf8/0x1c0
>   system_call_common+0xf0/0x278
>
> Fixes: cc90bc68422 ("block: fix "check bi_size overflow before merge"")
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
> ---
> RESEND: added "fixes" tag
>
>  block/bio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index a7366c02c9b5..675ecd81047b 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -877,8 +877,10 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
>                 struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
>
>                 if (page_is_mergeable(bv, page, len, off, same_page)) {
> -                       if (bio->bi_iter.bi_size > UINT_MAX - len)
> +                       if (bio->bi_iter.bi_size > UINT_MAX - len) {
> +                               *same_page = false;
>                                 return false;
> +                       }
>                         bv->bv_len += len;
>                         bio->bi_iter.bi_size += len;
>                         return true;

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming Lei