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Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid null pointer access when handling
 IPU error
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
References: <20210510142804.511265-1-jaegeuk@kernel.org>
 <9df7d088-3580-122b-60a3-799ea665cfeb@huawei.com>
 <YJoRCwwRDgEH49/P@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <f26b93fa-ac2d-0fa7-0ef5-5534558b84d7@huawei.com>
Date:   Tue, 11 May 2021 14:02:53 +0800
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On 2021/5/11 13:07, Jaegeuk Kim wrote:
> On 05/11, Chao Yu wrote:
>> On 2021/5/10 22:28, Jaegeuk Kim wrote:
>>>    Unable to handle kernel NULL pointer dereference at virtual address 000000000000001a
>>>    pc : f2fs_inplace_write_data+0x144/0x208
>>>    lr : f2fs_inplace_write_data+0x134/0x208
>>>    Call trace:
>>>     f2fs_inplace_write_data+0x144/0x208
>>>     f2fs_do_write_data_page+0x270/0x770
>>>     f2fs_write_single_data_page+0x47c/0x830
>>>     __f2fs_write_data_pages+0x444/0x98c
>>>     f2fs_write_data_pages.llvm.16514453770497736882+0x2c/0x38
>>>     do_writepages+0x58/0x118
>>>     __writeback_single_inode+0x44/0x300
>>>     writeback_sb_inodes+0x4b8/0x9c8
>>>     wb_writeback+0x148/0x42c
>>>     wb_do_writeback+0xc8/0x390
>>>     wb_workfn+0xb0/0x2f4
>>>     process_one_work+0x1fc/0x444
>>>     worker_thread+0x268/0x4b4
>>>     kthread+0x13c/0x158
>>>     ret_from_fork+0x10/0x18
>>>
>>> Fixes: 955772787667 ("f2fs: drop inplace IO if fs status is abnormal")
>>
>> My bad, thanks for fixing this.
>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>> ---
>>>    fs/f2fs/segment.c | 8 +++++---
>>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index c605415840b5..ae875557d693 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -3577,9 +3577,11 @@ int f2fs_inplace_write_data(struct f2fs_io_info *fio)
>>>    	if (fio->bio) {
>>>    		struct bio *bio = *(fio->bio);
>>> -		bio->bi_status = BLK_STS_IOERR;
>>> -		bio_endio(bio);
>>> -		fio->bio = NULL;
>>> +		if (bio) {
>>> +			bio->bi_status = BLK_STS_IOERR;
>>> +			bio_endio(bio);
>>> +			fio->bio = NULL;
>>
>> fio->bio points a bio assigned in writepages(), so it should reset
>> that bio to NULL by *(fio->bio) = NULL.
> 
> Good timing. I hit other kernel panic, and it seems this is the root cause.
> Let me give it a try. :)
> 
> --- v2 ---
> 
>   Unable to handle kernel NULL pointer dereference at virtual address 000000000000001a
>   pc : f2fs_inplace_write_data+0x144/0x208
>   lr : f2fs_inplace_write_data+0x134/0x208
>   Call trace:
>    f2fs_inplace_write_data+0x144/0x208
>    f2fs_do_write_data_page+0x270/0x770
>    f2fs_write_single_data_page+0x47c/0x830
>    __f2fs_write_data_pages+0x444/0x98c
>    f2fs_write_data_pages.llvm.16514453770497736882+0x2c/0x38
>    do_writepages+0x58/0x118
>    __writeback_single_inode+0x44/0x300
>    writeback_sb_inodes+0x4b8/0x9c8
>    wb_writeback+0x148/0x42c
>    wb_do_writeback+0xc8/0x390
>    wb_workfn+0xb0/0x2f4
>    process_one_work+0x1fc/0x444
>    worker_thread+0x268/0x4b4
>    kthread+0x13c/0x158
>    ret_from_fork+0x10/0x18
> 
> Fixes: 955772787667 ("f2fs: drop inplace IO if fs status is abnormal")
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,