Re: [f2fs-dev][PATCH RESEND] f2fs: avoid allocating failure in bio_alloc

[Gu Zheng]

Hi Chao,

On 09/16/2013 11:26 AM, Chao Yu wrote:

> Hi Gu
> 
>> -----Original Message-----
>> From: Gu Zheng [mailto:guz.fnst@xxxxxxxxxxxxxx]
>> Sent: Monday, September 16, 2013 10:09 AM
>> To: Chao Yu
>> Cc: Kim Jaegeuk; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx;
>> linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; 谭姝
>> Subject: Re: [f2fs-dev][PATCH RESEND] f2fs: avoid allocating failure in
> bio_alloc
>>
>> Hi Chao,
>>
>> On 09/13/2013 09:27 PM, Chao Yu wrote:
>>
>>> This patch add macro MAX_BIO_BLOCKS to limit value of npages in
>>> f2fs_bio_alloc, it can avoid allocating failure in bio_alloc caused by
>>> npages is larger than UIO_MAXIOV.
>>
>> As I know bio_alloc is based of *fs_bio_set* pool, without the limitation
> of
>> UIO_MAXIOV, am I missing something?
> 
> Here is the code in bio.c, fs_bio_set is as the actual parameter pass to bs
> without being inited.

fs_bio_set was initiated early in the bio subsystem init.

> So it may have opportunity to return NULL in this function.

It may be, but may not be the thread you mentioned below.

> ---
> Bio.c 
> struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set
> *bs)
> {
> ......
> 	if (!bs) {
> 		if (nr_iovecs > UIO_MAXIOV)
> 			return NULL;
> ---
> I did the abnormal test: modify the max_sectors_kb in /sys/block/sdx/queue
> to 32767 for a disk with f2fs format,
> and I got a segfualt in f2fs_bio_alloc after the img mounted.
> Is there anyting I missed?

Hmm, this change will also trigger bvec_alloc failed, did you add some traces
to debug this?

Regards,
Gu

> 
>>
>> Thanks,
>> Gu
>>
>>>
>>> Signed-off-by: Yu Chao <chao2.yu@xxxxxxxxxxx>
>>>  ---
>>>  fs/f2fs/segment.c |    4 +++-
>>>  fs/f2fs/segment.h |    3 +++
>>>  2 files changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index
>>> 09af9c7..bd79bbe 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -657,6 +657,7 @@ static void submit_write_page(struct f2fs_sb_info
>>> *sbi, struct page *page,
>>>                                 block_t blk_addr, enum page_type
>> type)
>>> {
>>>         struct block_device *bdev = sbi->sb->s_bdev;
>>> +       int bio_blocks;
>>>
>>>         verify_block_addr(sbi, blk_addr);
>>>
>>> @@ -676,7 +677,8 @@ retry:
>>>                         goto retry;
>>>                 }
>>>
>>> -               sbi->bio[type] = f2fs_bio_alloc(bdev,
> max_hw_blocks(sbi));
>>> +               bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
>>> +               sbi->bio[type] = f2fs_bio_alloc(bdev, bio_blocks);
>>>                 sbi->bio[type]->bi_sector = SECTOR_FROM_BLOCK(sbi,
>>> blk_addr);
>>>                 sbi->bio[type]->bi_private = priv;
>>>                 /*
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h index
>>> bdd10ea..6352af1 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -9,6 +9,7 @@
>>>   * published by the Free Software Foundation.
>>>   */
>>>  #include <linux/blkdev.h>
>>> +#include <linux/uio.h>
>>>
>>>  /* constant macro */
>>>  #define NULL_SEGNO                     ((unsigned int)(~0))
>>> @@ -90,6 +91,8 @@
>>>         (blk_addr << ((sbi)->log_blocksize - F2FS_LOG_SECTOR_SIZE))
>>>  #define SECTOR_TO_BLOCK(sbi, sectors)
>> \
>>>         (sectors >> ((sbi)->log_blocksize - F2FS_LOG_SECTOR_SIZE))
>>> +#define MAX_BIO_BLOCKS(max_hw_blocks)
>> \
>>> +       (min((int)max_hw_blocks, UIO_MAXIOV))
>>>
>>>  /* during checkpoint, bio_private is used to synchronize the last bio
>>> */  struct bio_private {
>>> ---
>>>
>>> --
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> 
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