On Fri, Sep 6, 2019 at 5:56 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > From: Michal Hocko <mhocko@xxxxxxxx> > > Thomas has noticed the following NULL ptr dereference when using cgroup > v1 kmem limit: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 > PGD 0 > P4D 0 > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 3 PID: 16923 Comm: gtk-update-icon Not tainted 4.19.51 #42 > Hardware name: Gigabyte Technology Co., Ltd. Z97X-Gaming G1/Z97X-Gaming G1, BIOS F9 07/31/2015 > RIP: 0010:create_empty_buffers+0x24/0x100 > Code: cd 0f 1f 44 00 00 0f 1f 44 00 00 41 54 49 89 d4 ba 01 00 00 00 55 53 48 89 fb e8 97 fe ff ff 48 89 c5 48 89 c2 eb 03 48 89 ca <48> 8b 4a 08 4c 09 22 48 85 c9 75 f1 48 89 6a 08 48 8b 43 18 48 8d > RSP: 0018:ffff927ac1b37bf8 EFLAGS: 00010286 > RAX: 0000000000000000 RBX: fffff2d4429fd740 RCX: 0000000100097149 > RDX: 0000000000000000 RSI: 0000000000000082 RDI: ffff9075a99fbe00 > RBP: 0000000000000000 R08: fffff2d440949cc8 R09: 00000000000960c0 > R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000 > R13: ffff907601f18360 R14: 0000000000002000 R15: 0000000000001000 > FS: 00007fb55b288bc0(0000) GS:ffff90761f8c0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000008 CR3: 000000007aebc002 CR4: 00000000001606e0 > Call Trace: > create_page_buffers+0x4d/0x60 > __block_write_begin_int+0x8e/0x5a0 > ? ext4_inode_attach_jinode.part.82+0xb0/0xb0 > ? jbd2__journal_start+0xd7/0x1f0 > ext4_da_write_begin+0x112/0x3d0 > generic_perform_write+0xf1/0x1b0 > ? file_update_time+0x70/0x140 > __generic_file_write_iter+0x141/0x1a0 > ext4_file_write_iter+0xef/0x3b0 > __vfs_write+0x17e/0x1e0 > vfs_write+0xa5/0x1a0 > ksys_write+0x57/0xd0 > do_syscall_64+0x55/0x160 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > Tetsuo then noticed that this is because the __memcg_kmem_charge_memcg > fails __GFP_NOFAIL charge when the kmem limit is reached. This is a > wrong behavior because nofail allocations are not allowed to fail. > Normal charge path simply forces the charge even if that means to cross > the limit. Kmem accounting should be doing the same. > > Reported-by: Thomas Lindroth <thomas.lindroth@xxxxxxxxx> > Debugged-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Cc: stable > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> I wonder what has changed since <http://lkml.kernel.org/r/20180525185501.82098-1-shakeelb@xxxxxxxxxx/>. > --- > mm/memcontrol.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 9ec5e12486a7..e18108b2b786 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2821,6 +2821,16 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order, > > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && > !page_counter_try_charge(&memcg->kmem, nr_pages, &counter)) { > + > + /* > + * Enforce __GFP_NOFAIL allocation because callers are not > + * prepared to see failures and likely do not have any failure > + * handling code. > + */ > + if (gfp & __GFP_NOFAIL) { > + page_counter_charge(&memcg->kmem, nr_pages); > + return 0; > + } > cancel_charge(memcg, nr_pages); > return -ENOMEM; > } > -- > 2.20.1 >
