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Qu Wenruo c53e965360 btrfs: qgroup: try to flush qgroup space when we get -EDQUOT 
[PROBLEM]
There are known problem related to how btrfs handles qgroup reserved
space.  One of the most obvious case is the the test case btrfs/153,
which do fallocate, then write into the preallocated range.

  btrfs/153 1s ... - output mismatch (see xfstests-dev/results//btrfs/153.out.bad)
      --- tests/btrfs/153.out     2019-10-22 15:18:14.068965341 +0800
      +++ xfstests-dev/results//btrfs/153.out.bad      2020-07-01 20:24:40.730000089 +0800
      @@ -1,2 +1,5 @@
       QA output created by 153
      +pwrite: Disk quota exceeded
      +/mnt/scratch/testfile2: Disk quota exceeded
      +/mnt/scratch/testfile2: Disk quota exceeded
       Silence is golden
      ...
      (Run 'diff -u xfstests-dev/tests/btrfs/153.out xfstests-dev/results//btrfs/153.out.bad'  to see the entire diff)

[CAUSE]
Since commit c6887cd111 ("Btrfs: don't do nocow check unless we have to"),
we always reserve space no matter if it's COW or not.

Such behavior change is mostly for performance, and reverting it is not
a good idea anyway.

For preallcoated extent, we reserve qgroup data space for it already,
and since we also reserve data space for qgroup at buffered write time,
it needs twice the space for us to write into preallocated space.

This leads to the -EDQUOT in buffered write routine.

And we can't follow the same solution, unlike data/meta space check,
qgroup reserved space is shared between data/metadata.
The EDQUOT can happen at the metadata reservation, so doing NODATACOW
check after qgroup reservation failure is not a solution.

[FIX]
To solve the problem, we don't return -EDQUOT directly, but every time
we got a -EDQUOT, we try to flush qgroup space:

- Flush all inodes of the root
  NODATACOW writes will free the qgroup reserved at run_dealloc_range().
  However we don't have the infrastructure to only flush NODATACOW
  inodes, here we flush all inodes anyway.

- Wait for ordered extents
  This would convert the preallocated metadata space into per-trans
  metadata, which can be freed in later transaction commit.

- Commit transaction
  This will free all per-trans metadata space.

Also we don't want to trigger flush multiple times, so here we introduce
a per-root wait list and a new root status, to ensure only one thread
starts the flushing.

Fixes: c6887cd111 ("Btrfs: don't do nocow check unless we have to")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
 		2020-07-27 12:55:42 +02:00
Documentation Char/misc driver fixes for 5.8-rc7 2020-07-26 09:33:25 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch Merge branch 'parisc-5.8-2' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux into master 2020-07-26 12:14:46 -07:00
block block-5.8-2020-07-10 2020-07-10 09:55:46 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto keys: asymmetric: fix error return code in software_key_query() 2020-07-15 15:49:04 -07:00
drivers Char/misc driver fixes for 5.8-rc7 2020-07-26 09:33:25 -07:00
fs btrfs: qgroup: try to flush qgroup space when we get -EDQUOT 2020-07-27 12:55:42 +02:00
include btrfs: use __u16 for the return value of btrfs_qgroup_level() 2020-07-27 12:55:37 +02:00
init kbuild: fix CONFIG_CC_CAN_LINK(_STATIC) for cross-compilation with Clang 2020-07-02 00:57:45 +09:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel Fix a interaction/regression between uprobes based shared library tracing & GDB. 2020-07-25 13:55:38 -07:00
lib RISC-V Fixes for 5.8-rc5 (ideally) 2020-07-11 19:22:46 -07:00
mm khugepaged: fix null-pointer dereference due to race 2020-07-24 12:42:41 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net into master 2020-07-25 11:50:59 -07:00
samples samples/vfs: avoid warning in statx override 2020-07-03 16:15:25 -07:00
scripts Kbuild fixes for v5.8 (3rd) 2020-07-26 13:46:57 -07:00
security integrity/ima: switch to using __kernel_read 2020-07-08 08:27:57 +02:00
sound sound fixes for 5.8-rc7 2020-07-21 08:06:45 -07:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net into master 2020-07-25 11:50:59 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt kvm: use more precise cast and do not drop __user 2020-07-02 05:39:31 -04:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Do not track `defconfig` from `make savedefconfig` 2020-07-05 16:15:46 +09:00
.mailmap mailmap: add entry for Mike Rapoport 2020-07-24 12:42:41 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge branch 'akpm' into master (patches from Andrew) 2020-07-24 14:24:35 -07:00
Makefile Linux 5.8-rc7 2020-07-26 14:14:06 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.