Re: [PATCH] f2fs: fix defragment writeback range truncation on 32-bit

[Chao Yu]

On 10/5/26 23:49, Zhan Xusheng wrote:
> f2fs_defragment_range() flushes the range it is about to defragment:
>
> 	filemap_write_and_wait_range(inode->i_mapping,
> 				pg_start << PAGE_SHIFT,
> 				(pg_end << PAGE_SHIFT) - 1);
>
> pg_start and pg_end are pgoff_t, 32 bits on 32-bit kernels, so both
> shifts are evaluated in 32 bits and truncated before they are widened to
> the loff_t parameters.  pg_end is only capped by the file's page count,
> so for a file larger than 4 GiB the shift wraps.
>
> For a 5 GiB file pg_end is 1310720 and the range collapses from
> [0, 5 GiB) to [0, 1 GiB), leaving the rest of the dirty pages unwritten
> before the blocks are moved.  For 8 GiB the shift yields 0, the minus one
> makes it (loff_t)-1, and the range becomes [0, LLONG_MAX].
>
> The matching call in f2fs_collapse_range() already casts:
>
> 	filemap_write_and_wait_range(inode->i_mapping,
> 				(loff_t)index << PAGE_SHIFT,
> 				((loff_t)pg_end << PAGE_SHIFT) - 1);
>
> Do the same here.  On i386 the shift changes from "shl $0xc,%ecx" to
> "shld", i.e. from a 32-bit shift to a double-precision one.

Cc: stable@xxxxxxxxxx

> Fixes: d323d005ac4a ("f2fs: support file defragment")
> Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,