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Baoquan He 08d1d0e6d0 memcg: only record foreign writebacks with dirty pages when memcg is not disabled 
In kdump kernel, memcg usually is disabled with 'cgroup_disable=memory'
for saving memory.  Now kdump kernel will always panic when dump vmcore
to local disk:

  BUG: kernel NULL pointer dereference, address: 0000000000000ab8
  Oops: 0000 [#1] SMP NOPTI
  CPU: 0 PID: 598 Comm: makedumpfile Not tainted 5.3.0+ #26
  Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 10/02/2018
  RIP: 0010:mem_cgroup_track_foreign_dirty_slowpath+0x38/0x140
  Call Trace:
   __set_page_dirty+0x52/0xc0
   iomap_set_page_dirty+0x50/0x90
   iomap_write_end+0x6e/0x270
   iomap_write_actor+0xce/0x170
   iomap_apply+0xba/0x11e
   iomap_file_buffered_write+0x62/0x90
   xfs_file_buffered_aio_write+0xca/0x320 [xfs]
   new_sync_write+0x12d/0x1d0
   vfs_write+0xa5/0x1a0
   ksys_write+0x59/0xd0
   do_syscall_64+0x59/0x1e0
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

And this will corrupt the 1st kernel too with 'cgroup_disable=memory'.

Via the trace and with debugging, it is pointing to commit 97b27821b4
("writeback, memcg: Implement foreign dirty flushing") which introduced
this regression.  Disabling memcg causes the null pointer dereference at
uninitialized data in function mem_cgroup_track_foreign_dirty_slowpath().

Fix it by returning directly if memcg is disabled, but not trying to
record the foreign writebacks with dirty pages.

Link: http://lkml.kernel.org/r/20190924141928.GD31919@MiWiFi-R3L-srv
Fixes: 97b27821b4 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-07 15:47:19 -07:00
arch Some MIPS fixes for the 5.4 cycle: 2019-10-04 13:31:56 -07:00
block block: sed-opal: fix sparse warning: convert __be64 data 2019-10-03 14:21:32 -06:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
Documentation dt-bindings: phy: lantiq: Fix Property Name 2019-10-02 14:14:58 -05:00
drivers xen: fixes and cleanups for 5.4-rc2 2019-10-04 11:13:09 -07:00
fs writeback: fix use-after-free in finish_writeback_work() 2019-10-07 15:47:19 -07:00
include memcg: only record foreign writebacks with dirty pages when memcg is not disabled 2019-10-07 15:47:19 -07:00
init Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel panic: ensure preemption is disabled during panic() 2019-10-07 15:47:19 -07:00
lib usercopy: Add parentheses around assignment in test_copy_struct_from_user 2019-10-03 21:13:27 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: fix -Wmissing-prototypes warnings 2019-10-07 15:47:19 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-28 17:47:33 -07:00
samples rpmsg updates for v5.4 2019-09-22 10:58:15 -07:00
scripts Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2019-09-27 19:37:27 -07:00
security Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
sound sound fixes for 5.4-rc1 2019-09-24 16:46:16 -07:00
tools ARM and x86 bugfixes of all kinds. The most visible one is that migrating 2019-10-04 11:17:51 -07:00
usr Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-28 17:47:33 -07:00
virt KVM/arm fixes for 5.4, take #1 2019-10-03 12:08:50 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2019-09-18 12:34:53 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS CREDITS: Update email address 2019-09-13 17:21:38 +03:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS kgdb patches for 5.4-rc2 2019-10-03 11:17:57 -07:00
Makefile Linux 5.4-rc1 2019-09-30 10:35:40 -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.