From: Baoquan He <bhe@xxxxxxxxxx>
Subject: 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
PGD 5fcab067 P4D 5fcab067 PUD 5ff73067 PMD 0
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
Code: 55 48 8b 2d 6a bd 12 01 53 4c 8b 67 38 0f 1f 44 00 00 49 8b 06 48 89 e9 31 db be ff ff ff ff 48 8b 38 49 8d 84 24 d0 0a 00 00 <48> 39 78 e8
74 5a 48 8b 50 f8 48 39 ca 79 0e 44 8b 00 41 83 f8 01
RSP: 0018:ffffbc9300817bd0 EFLAGS: 00010046
RAX: 0000000000000ad0 RBX: 0000000000000000 RCX: 00000000fffba227
RDX: fffffffffffffff8 RSI: 00000000ffffffff RDI: 0000000000000004
RBP: 00000000fffba227 R08: 0000000000030340 R09: ffffbc9300817d10
R10: 0000000000000000 R11: 0000000000001000 R12: 0000000000000000
R13: ffff999c1fa2bcf0 R14: ffff999c1f7bcc78 R15: ffffe51fc177a8c0
FS: 00007f84f14c2b80(0000) GS:ffff999c22200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000ab8 CR3: 000000005f564000 CR4: 00000000003406b0
Call Trace:
__set_page_dirty+0x52/0xc0
iomap_set_page_dirty+0x50/0x90
iomap_write_end+0x6e/0x270
iomap_write_actor+0xce/0x170
? iomap_write_end+0x270/0x270
iomap_apply+0xba/0x11e
? iomap_write_end+0x270/0x270
iomap_file_buffered_write+0x62/0x90
? iomap_write_end+0x270/0x270
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
RIP: 0033:0x7f84f1093ab5
And this will corrupt the 1st kernel too with 'cgroup_disable=memory'.
Via the trace and with debugging, it is pointing to commit 97b27821b485
("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: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 3 +++
1 file changed, 3 insertions(+)
--- a/include/linux/memcontrol.h~memcg-only-record-foreign-writebacks-with-dirty-pages-when-memcg-is-not-disabled
+++ a/include/linux/memcontrol.h
@@ -1264,6 +1264,9 @@ void mem_cgroup_track_foreign_dirty_slow
static inline void mem_cgroup_track_foreign_dirty(struct page *page,
struct bdi_writeback *wb)
{
+ if (mem_cgroup_disabled())
+ return;
+
if (unlikely(&page->mem_cgroup->css != wb->memcg_css))
mem_cgroup_track_foreign_dirty_slowpath(page, wb);
}
_
