linux/fs/nilfs2
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
..
alloc.c
alloc.h
bmap.c
bmap.h
btnode.c
btnode.h
btree.c
btree.h
cpfile.c
cpfile.h
dat.c
dat.h
dir.c
direct.c
direct.h
export.h
file.c
gcinode.c
ifile.c
ifile.h
inode.c A lot of bug fixes and cleanups for ext4, including: 2020-06-05 16:19:28 -07:00
ioctl.c
Kconfig
Makefile
mdt.c
mdt.h
namei.c
nilfs.h
page.c
page.h
recovery.c
segbuf.c
segbuf.h
segment.c nilfs2: fix null pointer dereference at nilfs_segctor_do_construct() 2020-06-10 19:14:17 -07:00
segment.h
sufile.c
sufile.h
super.c
sysfs.c
sysfs.h
the_nilfs.c
the_nilfs.h