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Qu Wenruo a12b877b55 btrfs: qgroup: Fix qgroup reserved space underflow caused by buffered write and quotas being enabled
[BUG]
Under the following case, we can underflow qgroup reserved space.

            Task A                |            Task B
---------------------------------------------------------------
 Quota disabled                   |
 Buffered write                   |
 |- btrfs_check_data_free_space() |
 |  *NO* qgroup space is reserved |
 |  since quota is *DISABLED*     |
 |- All pages are copied to page  |
    cache                         |
                                  | Enable quota
                                  | Quota scan finished
                                  |
                                  | Sync_fs
                                  | |- run_delalloc_range
                                  | |- Write pages
                                  | |- btrfs_finish_ordered_io
                                  |    |- insert_reserved_file_extent
                                  |       |- btrfs_qgroup_release_data()
                                  |          Since no qgroup space is
                                             reserved in Task A, we
                                             underflow qgroup reserved
                                             space
This can be detected by fstest btrfs/104.

[CAUSE]
In insert_reserved_file_extent() we tell qgroup to release the @ram_bytes
size of qgroup reserved_space in all cases.
And btrfs_qgroup_release_data() will check if quotas are enabled.

However in the above case, the buffered write happens before quota is
enabled, so we don't have the reserved space for that range.

[FIX]
In insert_reserved_file_extent(), we tell qgroup to release the acctual
byte number it released.
In the above case, since we don't have the reserved space, we tell
qgroups to release 0 byte, so the problem can be fixed.

And thanks to the @reserved parameter introduced by the qgroup rework,
and previous patch to return released bytes, the fix can be as small as
10 lines.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
[ changelog updates ]
Signed-off-by: David Sterba <dsterba@suse.com>
2017-06-29 20:17:02 +02:00
arch mm: larger stack guard gap, between vmas 2017-06-19 21:50:20 +08:00
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Documentation mm: larger stack guard gap, between vmas 2017-06-19 21:50:20 +08:00
drivers virtio: bugfix 2017-06-19 09:25:05 +09:00
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fs btrfs: qgroup: Fix qgroup reserved space underflow caused by buffered write and quotas being enabled 2017-06-29 20:17:02 +02:00
include Btrfs: btrfs_ioctl_search_key documentation 2017-06-19 18:26:03 +02:00
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kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-06-18 18:46:51 +09:00
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tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-06-18 18:42:31 +09:00
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Makefile Linux 4.12-rc6 2017-06-19 22:19:37 +08:00
README

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.