Re: [f2fs-dev] [PATCH] f2fs: fix fiemap failure issue when page size is 16KB

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 2024/10/29 14:15, Xiuhong Wang wrote:
> After enable 16K page size, an infinite loop may occur in
> fiemap (fm_length=UINT64_MAX) on a file, such as the 16KB
> scratch.img during the remount operation in Android.
> 
> The condition for whether fiemap continues to map is to check
> whether the number of bytes corresponding to the next map.m_lblk
> exceeds blks_to_bytes(inode,max_inode_blocks(inode)) if there are HOLE.
> The latter does not take into account the maximum size of a file with 16KB
> page size, so the loop cannot be jumped out.
> 
> The following is the fail trace:
> When f2fs_map_blocks reaches map.m_lblk=3936, it needs to go to the
> first direct node block, so the map is 3936 + 4090 = 8026,
> The next map is the second direct node block, that is,
> 8026 + 4090 = 12116,
> The next map is the first indirect node block, that is,
> 12116 + 4090 * 4090 = 16740216,
> The next map is the second indirect node block, that is,
> 16740216 + 4090 * 4090 = 33468316,
> The next map is the first double indirect node block, that is,
> 33468316 + 4090 * 4090 * 4090 = 68451397316
> Since map.m_lblk represents the address of a block, which is 32
> bits, truncation will occur, that is, 68451397316 becomes
> 4026887876, and the number of bytes corresponding to the block
> number does not exceed blks_to_bytes(inode,max_inode_blocks(inode)),
> so the loop will not be jumped out.
> The next time, it will be considered that it should still be a
> double indirect node block, that is,
> 4026887876 + 4090 * 4090 * 4090 = 72444816876, which will be
> truncated to 3725340140, and the loop will not be jumped out.
> 
> 156.374871: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 0, start blkaddr = 0x8e00, len = 0x200, flags = 2,seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.374916: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 512, start blkaddr = 0x0, len = 0x0, flags = 0 , seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.374920: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 513, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> ......
> 156.385747: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 3935, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385752: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 3936, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385755: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 8026, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385758: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 12116, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385761: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 16740216, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385764: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 33468316, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385767: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 4026887876, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385770: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 3725340140, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385772: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 4026887876, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 156.385775: f2fs_map_blocks: dev = (254,57), ino = 7449, file offset = 3725340140, start blkaddr = 0x0, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 1, err = 0
> 
> Commit a6a010f5def5 ("f2fs: Restrict max filesize for 16K f2fs")
> has set the maximum allowed file size to (U32_MAX + 1) * F2FS_BLKSIZE,
> so max_file_blocks should be used here to limit it, that is,
> maxbytes defined above. And the max_inode_blocks function is not
> called by other functions except here, so cleanup it.
> 
> Signed-off-by: Xiuhong Wang <xiuhong.wang@unisoc.com>
> Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,


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