| Message ID | 20190826101012.10575-4-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/memory_hotplug: Consider all zones when removing memory | expand |
On Mon 26-08-19 12:10:09, David Hildenbrand wrote: > It is easier than I though to trigger a kernel bug by removing memory that > was never onlined. With CONFIG_DEBUG_VM the memmap is initialized with > garbage, resulting in the detection of a broken zone when removing memory. > Without CONFIG_DEBUG_VM it is less likely - but we could still have > garbage in the memmap. > > :/# [ 23.912993] BUG: unable to handle page fault for address: 000000000000353d > [ 23.914219] #PF: supervisor write access in kernel mode > [ 23.915199] #PF: error_code(0x0002) - not-present page > [ 23.916160] PGD 0 P4D 0 > [ 23.916627] Oops: 0002 [#1] SMP PTI > [ 23.917256] CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.3.0-rc5-next-20190820+ #317 > [ 23.918900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 > [ 23.921194] Workqueue: kacpi_hotplug acpi_hotplug_work_fn > [ 23.922249] RIP: 0010:clear_zone_contiguous+0x5/0x10 > [ 23.923173] Code: 48 89 c6 48 89 c3 e8 2a fe ff ff 48 85 c0 75 cf 5b 5d c3 c6 85 fd 05 00 00 01 5b 5d c3 0f 1f 840 > [ 23.926876] RSP: 0018:ffffad2400043c98 EFLAGS: 00010246 > [ 23.927928] RAX: 0000000000000000 RBX: 0000000200000000 RCX: 0000000000000000 > [ 23.929458] RDX: 0000000000200000 RSI: 0000000000140000 RDI: 0000000000002f40 > [ 23.930899] RBP: 0000000140000000 R08: 0000000000000000 R09: 0000000000000001 > [ 23.932362] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 > [ 23.933603] R13: 0000000000140000 R14: 0000000000002f40 R15: ffff9e3e7aff3680 > [ 23.934913] FS: 0000000000000000(0000) GS:ffff9e3e7bb00000(0000) knlGS:0000000000000000 > [ 23.936294] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 23.937481] CR2: 000000000000353d CR3: 0000000058610000 CR4: 00000000000006e0 > [ 23.938687] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 23.939889] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 23.941168] Call Trace: > [ 23.941580] __remove_pages+0x4b/0x640 > [ 23.942303] ? mark_held_locks+0x49/0x70 > [ 23.943149] arch_remove_memory+0x63/0x8d > [ 23.943921] try_remove_memory+0xdb/0x130 > [ 23.944766] ? walk_memory_blocks+0x7f/0x9e > [ 23.945616] __remove_memory+0xa/0x11 > [ 23.946274] acpi_memory_device_remove+0x70/0x100 > [ 23.947308] acpi_bus_trim+0x55/0x90 > [ 23.947914] acpi_device_hotplug+0x227/0x3a0 > [ 23.948714] acpi_hotplug_work_fn+0x1a/0x30 > [ 23.949433] process_one_work+0x221/0x550 > [ 23.950190] worker_thread+0x50/0x3b0 > [ 23.950993] kthread+0x105/0x140 > [ 23.951644] ? process_one_work+0x550/0x550 > [ 23.952508] ? kthread_park+0x80/0x80 > [ 23.953367] ret_from_fork+0x3a/0x50 > [ 23.954025] Modules linked in: > [ 23.954613] CR2: 000000000000353d > [ 23.955248] ---[ end trace 93d982b1fb3e1a69 ]--- Yes, this is indeed nasty. I didin't think of this when separating memmap initialization from the hotremove. This means that the zone pointer is a garbage in arch_remove_memory already. The proper fix is to remove it from that level down. Moreover the zone is only needed for the shrinking code and zone continuous thingy. The later belongs to offlining code unless I am missing something. I can see that you are removing zone parameter in a later patch but wouldn't it be just better to remove the whole zone thing in a single patch and have this as a bug fix for a rare bug with a fixes tag?
On 29.08.19 17:39, Michal Hocko wrote: > On Mon 26-08-19 12:10:09, David Hildenbrand wrote: >> It is easier than I though to trigger a kernel bug by removing memory that >> was never onlined. With CONFIG_DEBUG_VM the memmap is initialized with >> garbage, resulting in the detection of a broken zone when removing memory. >> Without CONFIG_DEBUG_VM it is less likely - but we could still have >> garbage in the memmap. >> >> :/# [ 23.912993] BUG: unable to handle page fault for address: 000000000000353d >> [ 23.914219] #PF: supervisor write access in kernel mode >> [ 23.915199] #PF: error_code(0x0002) - not-present page >> [ 23.916160] PGD 0 P4D 0 >> [ 23.916627] Oops: 0002 [#1] SMP PTI >> [ 23.917256] CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.3.0-rc5-next-20190820+ #317 >> [ 23.918900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 >> [ 23.921194] Workqueue: kacpi_hotplug acpi_hotplug_work_fn >> [ 23.922249] RIP: 0010:clear_zone_contiguous+0x5/0x10 >> [ 23.923173] Code: 48 89 c6 48 89 c3 e8 2a fe ff ff 48 85 c0 75 cf 5b 5d c3 c6 85 fd 05 00 00 01 5b 5d c3 0f 1f 840 >> [ 23.926876] RSP: 0018:ffffad2400043c98 EFLAGS: 00010246 >> [ 23.927928] RAX: 0000000000000000 RBX: 0000000200000000 RCX: 0000000000000000 >> [ 23.929458] RDX: 0000000000200000 RSI: 0000000000140000 RDI: 0000000000002f40 >> [ 23.930899] RBP: 0000000140000000 R08: 0000000000000000 R09: 0000000000000001 >> [ 23.932362] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 >> [ 23.933603] R13: 0000000000140000 R14: 0000000000002f40 R15: ffff9e3e7aff3680 >> [ 23.934913] FS: 0000000000000000(0000) GS:ffff9e3e7bb00000(0000) knlGS:0000000000000000 >> [ 23.936294] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 23.937481] CR2: 000000000000353d CR3: 0000000058610000 CR4: 00000000000006e0 >> [ 23.938687] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> [ 23.939889] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> [ 23.941168] Call Trace: >> [ 23.941580] __remove_pages+0x4b/0x640 >> [ 23.942303] ? mark_held_locks+0x49/0x70 >> [ 23.943149] arch_remove_memory+0x63/0x8d >> [ 23.943921] try_remove_memory+0xdb/0x130 >> [ 23.944766] ? walk_memory_blocks+0x7f/0x9e >> [ 23.945616] __remove_memory+0xa/0x11 >> [ 23.946274] acpi_memory_device_remove+0x70/0x100 >> [ 23.947308] acpi_bus_trim+0x55/0x90 >> [ 23.947914] acpi_device_hotplug+0x227/0x3a0 >> [ 23.948714] acpi_hotplug_work_fn+0x1a/0x30 >> [ 23.949433] process_one_work+0x221/0x550 >> [ 23.950190] worker_thread+0x50/0x3b0 >> [ 23.950993] kthread+0x105/0x140 >> [ 23.951644] ? process_one_work+0x550/0x550 >> [ 23.952508] ? kthread_park+0x80/0x80 >> [ 23.953367] ret_from_fork+0x3a/0x50 >> [ 23.954025] Modules linked in: >> [ 23.954613] CR2: 000000000000353d >> [ 23.955248] ---[ end trace 93d982b1fb3e1a69 ]--- > > Yes, this is indeed nasty. I didin't think of this when separating > memmap initialization from the hotremove. This means that the zone > pointer is a garbage in arch_remove_memory already. The proper fix is to > remove it from that level down. Moreover the zone is only needed for the > shrinking code and zone continuous thingy. The later belongs to offlining > code unless I am missing something. I can see that you are removing zone > parameter in a later patch but wouldn't it be just better to remove the > whole zone thing in a single patch and have this as a bug fix for a rare > bug with a fixes tag? > If I remember correctly, this patch already fixed the issue for me, without the other cleanup (removing the zone parameter). But I might be wrong. Anyhow, I'll send a v4 shortly (either this evening or tomorrow), so you can safe yourself some review time and wait for that one :) I'll try to see if I can attach fixes tags to selected commits. But if it makes review harder, I prefer keeping this split (this has been broken for a long time either way).
On Thu 29-08-19 17:54:35, David Hildenbrand wrote: > On 29.08.19 17:39, Michal Hocko wrote: > > On Mon 26-08-19 12:10:09, David Hildenbrand wrote: > >> It is easier than I though to trigger a kernel bug by removing memory that > >> was never onlined. With CONFIG_DEBUG_VM the memmap is initialized with > >> garbage, resulting in the detection of a broken zone when removing memory. > >> Without CONFIG_DEBUG_VM it is less likely - but we could still have > >> garbage in the memmap. > >> > >> :/# [ 23.912993] BUG: unable to handle page fault for address: 000000000000353d > >> [ 23.914219] #PF: supervisor write access in kernel mode > >> [ 23.915199] #PF: error_code(0x0002) - not-present page > >> [ 23.916160] PGD 0 P4D 0 > >> [ 23.916627] Oops: 0002 [#1] SMP PTI > >> [ 23.917256] CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.3.0-rc5-next-20190820+ #317 > >> [ 23.918900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 > >> [ 23.921194] Workqueue: kacpi_hotplug acpi_hotplug_work_fn > >> [ 23.922249] RIP: 0010:clear_zone_contiguous+0x5/0x10 > >> [ 23.923173] Code: 48 89 c6 48 89 c3 e8 2a fe ff ff 48 85 c0 75 cf 5b 5d c3 c6 85 fd 05 00 00 01 5b 5d c3 0f 1f 840 > >> [ 23.926876] RSP: 0018:ffffad2400043c98 EFLAGS: 00010246 > >> [ 23.927928] RAX: 0000000000000000 RBX: 0000000200000000 RCX: 0000000000000000 > >> [ 23.929458] RDX: 0000000000200000 RSI: 0000000000140000 RDI: 0000000000002f40 > >> [ 23.930899] RBP: 0000000140000000 R08: 0000000000000000 R09: 0000000000000001 > >> [ 23.932362] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 > >> [ 23.933603] R13: 0000000000140000 R14: 0000000000002f40 R15: ffff9e3e7aff3680 > >> [ 23.934913] FS: 0000000000000000(0000) GS:ffff9e3e7bb00000(0000) knlGS:0000000000000000 > >> [ 23.936294] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >> [ 23.937481] CR2: 000000000000353d CR3: 0000000058610000 CR4: 00000000000006e0 > >> [ 23.938687] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > >> [ 23.939889] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > >> [ 23.941168] Call Trace: > >> [ 23.941580] __remove_pages+0x4b/0x640 > >> [ 23.942303] ? mark_held_locks+0x49/0x70 > >> [ 23.943149] arch_remove_memory+0x63/0x8d > >> [ 23.943921] try_remove_memory+0xdb/0x130 > >> [ 23.944766] ? walk_memory_blocks+0x7f/0x9e > >> [ 23.945616] __remove_memory+0xa/0x11 > >> [ 23.946274] acpi_memory_device_remove+0x70/0x100 > >> [ 23.947308] acpi_bus_trim+0x55/0x90 > >> [ 23.947914] acpi_device_hotplug+0x227/0x3a0 > >> [ 23.948714] acpi_hotplug_work_fn+0x1a/0x30 > >> [ 23.949433] process_one_work+0x221/0x550 > >> [ 23.950190] worker_thread+0x50/0x3b0 > >> [ 23.950993] kthread+0x105/0x140 > >> [ 23.951644] ? process_one_work+0x550/0x550 > >> [ 23.952508] ? kthread_park+0x80/0x80 > >> [ 23.953367] ret_from_fork+0x3a/0x50 > >> [ 23.954025] Modules linked in: > >> [ 23.954613] CR2: 000000000000353d > >> [ 23.955248] ---[ end trace 93d982b1fb3e1a69 ]--- > > > > Yes, this is indeed nasty. I didin't think of this when separating > > memmap initialization from the hotremove. This means that the zone > > pointer is a garbage in arch_remove_memory already. The proper fix is to > > remove it from that level down. Moreover the zone is only needed for the > > shrinking code and zone continuous thingy. The later belongs to offlining > > code unless I am missing something. I can see that you are removing zone > > parameter in a later patch but wouldn't it be just better to remove the > > whole zone thing in a single patch and have this as a bug fix for a rare > > bug with a fixes tag? > > > > If I remember correctly, this patch already fixed the issue for me, That might be the case because nothing else does access zone on the way. But the pointer is simply bogus. Removing it is the proper way to fix it. And I argue that zone shouldn't even be necessary. Re-evaluating continuous status of the zone is really something for offlining phase. Check how we use pfn_to_online_page there. > without the other cleanup (removing the zone parameter). But I might be > wrong. > > Anyhow, I'll send a v4 shortly (either this evening or tomorrow), so you > can safe yourself some review time and wait for that one :) No rush, really... It seems this is quite unlikely event as most hotplug usecases simply online memory before removing it later on.
On 29.08.19 18:27, Michal Hocko wrote: > On Thu 29-08-19 17:54:35, David Hildenbrand wrote: >> On 29.08.19 17:39, Michal Hocko wrote: >>> On Mon 26-08-19 12:10:09, David Hildenbrand wrote: >>>> It is easier than I though to trigger a kernel bug by removing memory that >>>> was never onlined. With CONFIG_DEBUG_VM the memmap is initialized with >>>> garbage, resulting in the detection of a broken zone when removing memory. >>>> Without CONFIG_DEBUG_VM it is less likely - but we could still have >>>> garbage in the memmap. >>>> >>>> :/# [ 23.912993] BUG: unable to handle page fault for address: 000000000000353d >>>> [ 23.914219] #PF: supervisor write access in kernel mode >>>> [ 23.915199] #PF: error_code(0x0002) - not-present page >>>> [ 23.916160] PGD 0 P4D 0 >>>> [ 23.916627] Oops: 0002 [#1] SMP PTI >>>> [ 23.917256] CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.3.0-rc5-next-20190820+ #317 >>>> [ 23.918900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 >>>> [ 23.921194] Workqueue: kacpi_hotplug acpi_hotplug_work_fn >>>> [ 23.922249] RIP: 0010:clear_zone_contiguous+0x5/0x10 >>>> [ 23.923173] Code: 48 89 c6 48 89 c3 e8 2a fe ff ff 48 85 c0 75 cf 5b 5d c3 c6 85 fd 05 00 00 01 5b 5d c3 0f 1f 840 >>>> [ 23.926876] RSP: 0018:ffffad2400043c98 EFLAGS: 00010246 >>>> [ 23.927928] RAX: 0000000000000000 RBX: 0000000200000000 RCX: 0000000000000000 >>>> [ 23.929458] RDX: 0000000000200000 RSI: 0000000000140000 RDI: 0000000000002f40 >>>> [ 23.930899] RBP: 0000000140000000 R08: 0000000000000000 R09: 0000000000000001 >>>> [ 23.932362] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 >>>> [ 23.933603] R13: 0000000000140000 R14: 0000000000002f40 R15: ffff9e3e7aff3680 >>>> [ 23.934913] FS: 0000000000000000(0000) GS:ffff9e3e7bb00000(0000) knlGS:0000000000000000 >>>> [ 23.936294] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> [ 23.937481] CR2: 000000000000353d CR3: 0000000058610000 CR4: 00000000000006e0 >>>> [ 23.938687] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>>> [ 23.939889] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>>> [ 23.941168] Call Trace: >>>> [ 23.941580] __remove_pages+0x4b/0x640 >>>> [ 23.942303] ? mark_held_locks+0x49/0x70 >>>> [ 23.943149] arch_remove_memory+0x63/0x8d >>>> [ 23.943921] try_remove_memory+0xdb/0x130 >>>> [ 23.944766] ? walk_memory_blocks+0x7f/0x9e >>>> [ 23.945616] __remove_memory+0xa/0x11 >>>> [ 23.946274] acpi_memory_device_remove+0x70/0x100 >>>> [ 23.947308] acpi_bus_trim+0x55/0x90 >>>> [ 23.947914] acpi_device_hotplug+0x227/0x3a0 >>>> [ 23.948714] acpi_hotplug_work_fn+0x1a/0x30 >>>> [ 23.949433] process_one_work+0x221/0x550 >>>> [ 23.950190] worker_thread+0x50/0x3b0 >>>> [ 23.950993] kthread+0x105/0x140 >>>> [ 23.951644] ? process_one_work+0x550/0x550 >>>> [ 23.952508] ? kthread_park+0x80/0x80 >>>> [ 23.953367] ret_from_fork+0x3a/0x50 >>>> [ 23.954025] Modules linked in: >>>> [ 23.954613] CR2: 000000000000353d >>>> [ 23.955248] ---[ end trace 93d982b1fb3e1a69 ]--- >>> >>> Yes, this is indeed nasty. I didin't think of this when separating >>> memmap initialization from the hotremove. This means that the zone >>> pointer is a garbage in arch_remove_memory already. The proper fix is to >>> remove it from that level down. Moreover the zone is only needed for the >>> shrinking code and zone continuous thingy. The later belongs to offlining >>> code unless I am missing something. I can see that you are removing zone >>> parameter in a later patch but wouldn't it be just better to remove the >>> whole zone thing in a single patch and have this as a bug fix for a rare >>> bug with a fixes tag? >>> >> >> If I remember correctly, this patch already fixed the issue for me, > > That might be the case because nothing else does access zone on the way. > But the pointer is simply bogus. Removing it is the proper way to fix > it. And I argue that zone shouldn't even be necessary. Re-evaluating > continuous status of the zone is really something for offlining phase. > Check how we use pfn_to_online_page there. Yeah I'm with you, I think you spotted patch 6/6 of this series and v3 already that does exactly that. It's just a matter of rearranging things. > >> without the other cleanup (removing the zone parameter). But I might be >> wrong. >> >> Anyhow, I'll send a v4 shortly (either this evening or tomorrow), so you >> can safe yourself some review time and wait for that one :) > > No rush, really... It seems this is quite unlikely event as most hotplug > usecases simply online memory before removing it later on. > I can trigger it reliably right now while working/testing virtio-mem, so I finally want to clean up this mess :) (has been on my list for a long time). I'll try to hunt for the right commit id's that broke it.
On Thu 29-08-19 18:59:31, David Hildenbrand wrote: > On 29.08.19 18:27, Michal Hocko wrote: [...] > > No rush, really... It seems this is quite unlikely event as most hotplug > > usecases simply online memory before removing it later on. > > > > I can trigger it reliably right now while working/testing virtio-mem, so > I finally want to clean up this mess :) (has been on my list for a long > time). I'll try to hunt for the right commit id's that broke it. f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")
On 30.08.19 08:01, Michal Hocko wrote: > On Thu 29-08-19 18:59:31, David Hildenbrand wrote: >> On 29.08.19 18:27, Michal Hocko wrote: > [...] >>> No rush, really... It seems this is quite unlikely event as most hotplug >>> usecases simply online memory before removing it later on. >>> >> >> I can trigger it reliably right now while working/testing virtio-mem, so >> I finally want to clean up this mess :) (has been on my list for a long >> time). I'll try to hunt for the right commit id's that broke it. > > f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to > zones until online") > Right, I can see that that commit still does a set_page_node(page, nid); SetPageReserved(page); for every added page. But of course the zone_idx might contain garbage. So for this garbage pointer, f1dd2cd13c4b seems to be the right one. Regarding shrink_zone_span(), I suspect it was introduced by d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
On Fri 30-08-19 08:20:32, David Hildenbrand wrote: [...] > Regarding shrink_zone_span(), I suspect it was introduced by > > d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug") zone shrinking code is much older - 815121d2b5cd5. But I do not think this is really needed for Fixes tag.
On 30.08.19 08:47, Michal Hocko wrote: > On Fri 30-08-19 08:20:32, David Hildenbrand wrote: > [...] >> Regarding shrink_zone_span(), I suspect it was introduced by >> >> d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug") > > zone shrinking code is much older - 815121d2b5cd5. But I do not think > this is really needed for Fixes tag. > Yes it's older, but since d0dc12e86b31 we could run into uninitialized nids for added memory when trying to shrink the zone.
On Fri 30-08-19 09:07:59, David Hildenbrand wrote: > On 30.08.19 08:47, Michal Hocko wrote: > > On Fri 30-08-19 08:20:32, David Hildenbrand wrote: > > [...] > >> Regarding shrink_zone_span(), I suspect it was introduced by > >> > >> d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug") > > > > zone shrinking code is much older - 815121d2b5cd5. But I do not think > > this is really needed for Fixes tag. > > > > Yes it's older, but since d0dc12e86b31 we could run into uninitialized > nids for added memory when trying to shrink the zone. Well, not really. Strictly speaking pre d0dc12e86b31 would initialize struct page to zero so it is initialized but that doesn't mean that the struct page has a meaningfull and usable content. Zone index would be 0 so the lowest zone which is not something you want to use on the hotremove path.
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 71779b7b14df..27f0457b7512 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -505,22 +505,28 @@ static void __remove_zone(struct zone *zone, unsigned long start_pfn, struct pglist_data *pgdat = zone->zone_pgdat; unsigned long flags; + if (!zone_intersects(zone, start_pfn, nr_pages)) + return; + pgdat_resize_lock(zone->zone_pgdat, &flags); shrink_zone_span(zone, start_pfn, start_pfn + nr_pages); shrink_pgdat_span(pgdat, start_pfn, start_pfn + nr_pages); pgdat_resize_unlock(zone->zone_pgdat, &flags); } -static void __remove_section(struct zone *zone, unsigned long pfn, - unsigned long nr_pages, unsigned long map_offset, - struct vmem_altmap *altmap) +static void __remove_section(unsigned long pfn, unsigned long nr_pages, + unsigned long map_offset, + struct vmem_altmap *altmap) { struct mem_section *ms = __nr_to_section(pfn_to_section_nr(pfn)); + struct zone *zone; if (WARN_ON_ONCE(!valid_section(ms))) return; - __remove_zone(zone, pfn, nr_pages); + /* TODO: move zone handling out of memory removal path */ + for_each_zone(zone) + __remove_zone(zone, pfn, nr_pages); sparse_remove_section(ms, pfn, nr_pages, map_offset, altmap); } @@ -547,7 +553,10 @@ void __remove_pages(struct zone *zone, unsigned long pfn, map_offset = vmem_altmap_offset(altmap); - clear_zone_contiguous(zone); + /* TODO: move zone handling out of memory removal path */ + for_each_zone(zone) + if (zone_intersects(zone, pfn, nr_pages)) + clear_zone_contiguous(zone); start_sec = pfn_to_section_nr(pfn); end_sec = pfn_to_section_nr(pfn + nr_pages - 1); @@ -557,13 +566,15 @@ void __remove_pages(struct zone *zone, unsigned long pfn, cond_resched(); pfns = min(nr_pages, PAGES_PER_SECTION - (pfn & ~PAGE_SECTION_MASK)); - __remove_section(zone, pfn, pfns, map_offset, altmap); + __remove_section(pfn, pfns, map_offset, altmap); pfn += pfns; nr_pages -= pfns; map_offset = 0; } - set_zone_contiguous(zone); + /* TODO: move zone handling out of memory removal path */ + for_each_zone(zone) + set_zone_contiguous(zone); } int set_online_page_callback(online_page_callback_t callback)
It is easier than I though to trigger a kernel bug by removing memory that was never onlined. With CONFIG_DEBUG_VM the memmap is initialized with garbage, resulting in the detection of a broken zone when removing memory. Without CONFIG_DEBUG_VM it is less likely - but we could still have garbage in the memmap. :/# [ 23.912993] BUG: unable to handle page fault for address: 000000000000353d [ 23.914219] #PF: supervisor write access in kernel mode [ 23.915199] #PF: error_code(0x0002) - not-present page [ 23.916160] PGD 0 P4D 0 [ 23.916627] Oops: 0002 [#1] SMP PTI [ 23.917256] CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.3.0-rc5-next-20190820+ #317 [ 23.918900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 [ 23.921194] Workqueue: kacpi_hotplug acpi_hotplug_work_fn [ 23.922249] RIP: 0010:clear_zone_contiguous+0x5/0x10 [ 23.923173] Code: 48 89 c6 48 89 c3 e8 2a fe ff ff 48 85 c0 75 cf 5b 5d c3 c6 85 fd 05 00 00 01 5b 5d c3 0f 1f 840 [ 23.926876] RSP: 0018:ffffad2400043c98 EFLAGS: 00010246 [ 23.927928] RAX: 0000000000000000 RBX: 0000000200000000 RCX: 0000000000000000 [ 23.929458] RDX: 0000000000200000 RSI: 0000000000140000 RDI: 0000000000002f40 [ 23.930899] RBP: 0000000140000000 R08: 0000000000000000 R09: 0000000000000001 [ 23.932362] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 [ 23.933603] R13: 0000000000140000 R14: 0000000000002f40 R15: ffff9e3e7aff3680 [ 23.934913] FS: 0000000000000000(0000) GS:ffff9e3e7bb00000(0000) knlGS:0000000000000000 [ 23.936294] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 23.937481] CR2: 000000000000353d CR3: 0000000058610000 CR4: 00000000000006e0 [ 23.938687] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 23.939889] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 23.941168] Call Trace: [ 23.941580] __remove_pages+0x4b/0x640 [ 23.942303] ? mark_held_locks+0x49/0x70 [ 23.943149] arch_remove_memory+0x63/0x8d [ 23.943921] try_remove_memory+0xdb/0x130 [ 23.944766] ? walk_memory_blocks+0x7f/0x9e [ 23.945616] __remove_memory+0xa/0x11 [ 23.946274] acpi_memory_device_remove+0x70/0x100 [ 23.947308] acpi_bus_trim+0x55/0x90 [ 23.947914] acpi_device_hotplug+0x227/0x3a0 [ 23.948714] acpi_hotplug_work_fn+0x1a/0x30 [ 23.949433] process_one_work+0x221/0x550 [ 23.950190] worker_thread+0x50/0x3b0 [ 23.950993] kthread+0x105/0x140 [ 23.951644] ? process_one_work+0x550/0x550 [ 23.952508] ? kthread_park+0x80/0x80 [ 23.953367] ret_from_fork+0x3a/0x50 [ 23.954025] Modules linked in: [ 23.954613] CR2: 000000000000353d [ 23.955248] ---[ end trace 93d982b1fb3e1a69 ]--- But the problem is more extreme: When removing memory we could have - Single memory blocks that fall into no zone (never onlined) - Single memory blocks that fall into multiple zones (offlined+re-onlined) - Multiple memory blocks that fall into different zones Right now, the zones don't get updated properly in these cases. So let's simply process all zones for now until we can properly handle this via the reverse of move_pfn_range_to_zone() (which would then be called something like remove_pfn_range_from_zone()), for example, when offlining memory or before removing ZONE_DEVICE memory. To speed things up, only mark applicable zones non-contiguous (and therefore reduce the zones to recompute) and skip non-intersecting zones when trying to resize. shrink_zone_span() and shrink_pgdat_span() seem to be able to cope just fine with pfn ranges they don't actually contain (but still intersect with). Don't check for zone_intersects() when triggering set_zone_contiguous() - we might have resized the zone and the check might no longer hold. For now, we have to try to recompute any zone (which will be skipped in case the zone is already contiguous). Note1: Detecting which memory is still part of a zone is not easy before removing memory as the detection relies almost completely on pfn_valid() right now. pfn_online() cannot be used as ZONE_DEVICE memory is never online. pfn_present() cannot be used as all memory is present once it was added (but not onlined). We need to rethink/refactor this properly. Note2: We are safe to call zone_intersects() without locking (as already done by onlining code in default_zone_for_pfn()), as we are protected by the memory hotplug lock - just like zone->contiguous. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Wei Yang <richardw.yang@linux.intel.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/memory_hotplug.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-)