On Tue 24-09-19 22:19:28, Baoquan He wrote:
> 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'.
>
> >From 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.
>
> Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Looks good to me. This is essentially the same thing as if MEMCG was
disabled completely AFAICS.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> v2->v3:
> Move the checking into mem_cgroup_track_foreign_dirty() per Michal's
> suggestions.
>
> include/linux/memcontrol.h | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index ad8f1a397ae4..0e0432dfac4d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1261,6 +1261,9 @@ 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);
> }
> --
> 2.17.2
--
Michal Hocko
SUSE Labs
