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authorBaoquan He <bhe@redhat.com>2019-10-06 17:58:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-10-07 15:47:19 -0700
commit08d1d0e6d0a00c6e687201774f3bf61177741e80 (patch)
tree36ed19a744ffc077db0066698ff7390000d76ac9
parent758b8db4a56ab03eca4ecbfa7fa641ed30fb2a90 (diff)
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 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@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>
-rw-r--r--include/linux/memcontrol.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 9b60863429cc..98380779f6d5 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1264,6 +1264,9 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
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);
}