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In commitd77815461f("btrfs: Avoid trucating page or punching hole in a already existed hole."), existing holes can be skipped by calling find_first_non_hole() to adjust start and len. However, if the given len is invalid and large, when an EXTENT_MAP_HOLE extent is found, len will not be set to zero because (em->start + em->len) is less than (start + len). Then the ret will be 1 but len will not be set to 0. The propagated non-zero ret will result in fallocate failure. In the while-loop of btrfs_replace_file_extents(), len is not updated every time before it calls find_first_non_hole(). That is, after btrfs_drop_extents() successfully drops the last non-hole file extent, it may fail with ENOSPC when attempting to drop a file extent item representing a hole. The problem can happen. After it calls find_first_non_hole(), the cur_offset will be adjusted to be larger than or equal to end. However, since the len is not set to zero, the break-loop condition (ret && !len) will not be met. After it leaves the while-loop, fallocate will return 1, which is an unexpected return value. We're not able to construct a reproducible way to let btrfs_drop_extents() fail with ENOSPC after it drops the last non-hole file extent but with remaining holes left. However, it's quite easy to fix. We just need to update and check the len every time before we call find_first_non_hole(). To make the while loop more readable, we also pull the variable updates to the bottom of loop like this: while (cur_offset < end) { ... // update cur_offset & len // advance cur_offset & len in hole-punching case if needed } Reported-by: Robbie Ko <robbieko@synology.com> Fixes:d77815461f("btrfs: Avoid trucating page or punching hole in a already existed hole.") CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Robbie Ko <robbieko@synology.com> Reviewed-by: Chung-Chiang Cheng <cccheng@synology.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: BingJing Chang <bingjingc@synology.com> Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.