Re: [PATCH v3] mm/memory_hotplug: refrain from adding memory into an impossible node

On 15.04.20 01:58, Vishal Verma wrote: > A misbehaving qemu created a situation where the ACPI SRAT table > advertised one fewer proximity domains than intended. The NFIT table did > describe all the expected proximity domains. This caused the device dax > driver to assign an impossible target_node to the device, and when > hotplugged as system memory, this would fail with the following > signature: > > [ +0.001627] BUG: kernel NULL pointer dereference, address: 0000000000000088 > [ +0.001331] #PF: supervisor read access in kernel mode > [ +0.000975] #PF: error_code(0x0000) - not-present page > [ +0.000976] PGD 80000001767d4067 P4D 80000001767d4067 PUD 10e0c4067 PMD 0 > [ +0.001338] Oops: 0000 [#1] SMP PTI > [ +0.000676] CPU: 4 PID: 22737 Comm: kswapd3 Tainted: G O 5.6.0-rc5 #9 > [ +0.001457] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 > [ +0.001990] RIP: 0010:prepare_kswapd_sleep+0x7c/0xc0 > [ +0.000780] Code: 89 df e8 87 fd ff ff 89 c2 31 c0 84 d2 74 e6 0f 1f 44 > 00 00 48 8b 05 fb af 7a 01 48 63 93 88 1d 01 00 48 8b > 84 d0 20 0f 00 00 <48> 3b 98 88 00 00 00 75 28 f0 80 a0 > 80 00 00 00 fe f0 80 a3 38 20 > [ +0.002877] RSP: 0018:ffffc900017a3e78 EFLAGS: 00010202 > [ +0.000805] RAX: 0000000000000000 RBX: ffff8881209e0000 RCX: 0000000000000000 > [ +0.001115] RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff8881209e0e80 > [ +0.001098] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000008000 > [ +0.001092] R10: 0000000000000000 R11: 0000000000000003 R12: 0000000000000003 > [ +0.001092] R13: 0000000000000003 R14: 0000000000000000 R15: ffffc900017a3ec8 > [ +0.001091] FS: 0000000000000000(0000) GS:ffff888318c00000(0000) knlGS:0000000000000000 > [ +0.001275] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ +0.000882] CR2: 0000000000000088 CR3: 0000000120b50002 CR4: 00000000001606e0 > [ +0.001095] Call Trace: > [ +0.000388] kswapd+0x103/0x520 > [ +0.000494] ? finish_wait+0x80/0x80 > [ +0.000547] ? balance_pgdat+0x5a0/0x5a0 > [ +0.000607] kthread+0x120/0x140 > [ +0.000508] ? kthread_create_on_node+0x60/0x60 > [ +0.000706] ret_from_fork+0x3a/0x50 > > Add a check in the add_memory path to ensure that the node to which we > are adding memory is in the node_possible_map > > Cc: David Hildenbrand <david(a)redhat.com&gt; > Cc: Dan Williams <dan.j.williams(a)intel.com&gt; > Cc: Dave Hansen <dave.hansen(a)linux.intel.com&gt; > Signed-off-by: Vishal Verma <vishal.l.verma(a)intel.com&gt; > --- > mm/memory_hotplug.c | 28 ++++++++++++++++++++++++++++ > 1 file changed, 28 insertions(+) > > v2: > - Centralize the check in the add_memory path (David) > - Instead of failing, add the memory to a nearby node, while warning > (and tainting) to call out attention to the firmware bug (Dan) > > v3: > - Fix the CONFIG_NUMA=n case, and use node 0 as the final fallback (Dan) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 0a54ffac8c68..536a809d6ebb 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -980,6 +980,30 @@ static int check_hotplug_memory_range(u64 start, u64 size) > return 0; > } > > +/* > + * Check that the node provided for adding memory was valid. > + * If not, find the nearest valid node and add the memory there while > + * tainting the kernel and displaying a warning to bring attention to the > + * underlying firmware problem. > + * Return nid if valid, or an adjusted node number that can be used instead > + * if the original nid was not valid > + */ -ETOOMUCHDOCUMENTAION "If the given node cannot be used (!node_possible()), return the nearest possible node and WARN_TAINT() about firmware issues." > +static int check_hotplug_node(int nid) > +{ > + int alt_nid; > + > + if (node_possible(nid)) > + return nid; > + > + alt_nid = numa_map_to_online_node(nid); > + if (alt_nid == NUMA_NO_NODE) > + alt_nid = first_online_node; > + WARN_TAINT(1, TAINT_FIRMWARE_WORKAROUND, > + "node %d expected, but was absent from the node_possible_map, using %d instead\n", > + nid, alt_nid); > + return alt_nid; > +} > + > static int online_memory_block(struct memory_block *mem, void *arg) > { > return device_online(&mem->dev); > @@ -1005,6 +1029,10 @@ int __ref add_memory_resource(int nid, struct resource *res) > if (ret) > return ret; > > + nid = check_hotplug_node(nid); > + if (nid < 0) > + return -ENXIO; > + > mem_hotplug_begin(); > > /* > You should do the same on the memory removal path.