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Ryusuke Konishi 8301c719a2 nilfs2: fix null pointer dereference at nilfs_segctor_do_construct() 
After commit c3aab9a0bd ("mm/filemap.c: don't initiate writeback if
mapping has no dirty pages"), the following null pointer dereference has
been reported on nilfs2:

  BUG: kernel NULL pointer dereference, address: 00000000000000a8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP PTI
  ...
  RIP: 0010:percpu_counter_add_batch+0xa/0x60
  ...
  Call Trace:
    __test_set_page_writeback+0x2d3/0x330
    nilfs_segctor_do_construct+0x10d3/0x2110 [nilfs2]
    nilfs_segctor_construct+0x168/0x260 [nilfs2]
    nilfs_segctor_thread+0x127/0x3b0 [nilfs2]
    kthread+0xf8/0x130
    ...

This crash turned out to be caused by set_page_writeback() call for
segment summary buffers at nilfs_segctor_prepare_write().

set_page_writeback() can call inc_wb_stat(inode_to_wb(inode),
WB_WRITEBACK) where inode_to_wb(inode) is NULL if the inode of
underlying block device does not have an associated wb.

This fixes the issue by calling inode_attach_wb() in advance to ensure
to associate the bdev inode with its wb.

Fixes: c3aab9a0bd ("mm/filemap.c: don't initiate writeback if mapping has no dirty pages")
Reported-by: Walton Hoops <me@waltonhoops.com>
Reported-by: Tomas Hlavaty <tom@logand.com>
Reported-by: ARAI Shun-ichi <hermes@ceres.dti.ne.jp>
Reported-by: Hideki EIRAKU <hdk1983@gmail.com>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>	[5.4+]
Link: http://lkml.kernel.org/r/20200608.011819.1399059588922299158.konishi.ryusuke@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-10 19:14:17 -07:00
arch This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
block for-5.8/drivers-2020-06-01 2020-06-02 15:37:03 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: engine - do not requeue in case of fatal error 2020-05-28 17:27:52 +10:00
Documentation This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
drivers This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
fs nilfs2: fix null pointer dereference at nilfs_segctor_do_construct() 2020-06-10 19:14:17 -07:00
include This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
init mm: don't include asm/pgtable.h if linux/mm.h is already included 2020-06-09 09:39:13 -07:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel kcov: check kcov_softirq in kcov_remote_stop() 2020-06-10 19:14:17 -07:00
lib lib/lz4/lz4_decompress.c: document deliberate use of `&' 2020-06-10 19:14:17 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm maccess: return -ERANGE when probe_kernel_read() fails 2020-06-09 09:39:16 -07:00
net mmap locking API: convert mmap_sem API comments 2020-06-09 09:39:14 -07:00
samples Kbuild updates for v5.8 2020-06-06 12:00:25 -07:00
scripts scripts/spelling: add a few more typos 2020-06-10 19:14:17 -07:00
security overlayfs update for 5.8 2020-06-09 15:40:50 -07:00
sound mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
tools khugepaged: selftests: fix timeout condition in wait_for_scan() 2020-06-10 19:14:17 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
.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 modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -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 This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
Makefile Kbuild updates for v5.8 2020-06-06 12:00:25 -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.