From: Balbir Singh <bsingharora@gmail.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
catalin.marinas@arm.com, will@kernel.org
Cc: mark.rutland@arm.com, mhocko@suse.com, ira.weiny@intel.com,
david@redhat.com, cai@lca.pw, logang@deltatee.com,
cpandya@codeaurora.org, arunks@codeaurora.org,
dan.j.williams@intel.com, mgorman@techsingularity.net,
osalvador@suse.de, ard.biesheuvel@arm.com, steve.capper@arm.com,
broonie@kernel.org, valentin.schneider@arm.com,
Robin.Murphy@arm.com, steven.price@arm.com,
suzuki.poulose@arm.com
Subject: Re: [PATCH V7 1/3] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove_memory()
Date: Mon, 16 Sep 2019 11:44:50 +1000 [thread overview]
Message-ID: <74bcbd36-3bec-be67-917d-60cd74cbcef0@gmail.com> (raw)
In-Reply-To: <1567503958-25831-2-git-send-email-anshuman.khandual@arm.com>
On 3/9/19 7:45 pm, Anshuman Khandual wrote:
> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
I could not find this path in the code, the only called for get_nid_for_pfn()
was register_mem_sect_under_node() when the system is under boot.
> entries between memory block and node. It first checks pfn validity with
> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
> (arm64 has this enabled) pfn_valid_within() calls pfn_valid().
>
> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
> which scans all mapped memblock regions with memblock_is_map_memory(). This
> creates a problem in memory hot remove path which has already removed given
> memory range from memory block with memblock_[remove|free] before arriving
> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
> of existing sysfs entries.
>
> [ 62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0
> [ 62.052517] ------------[ cut here ]------------
This seems like arm64 is not ready for probe_store() via drivers/base/memory.c/ode.c
> [ 62.053211] kernel BUG at mm/memory_hotplug.c:1143!
> [ 62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> [ 62.054589] Modules linked in:
> [ 62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41
> [ 62.056274] Hardware name: linux,dummy-virt (DT)
> [ 62.057166] pstate: 40400005 (nZcv daif +PAN -UAO)
> [ 62.058083] pc : add_memory_resource+0x1cc/0x1d8
> [ 62.058961] lr : add_memory_resource+0x10c/0x1d8
> [ 62.059842] sp : ffff0000168b3ce0
> [ 62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00
> [ 62.061501] x27: 0000000000000000 x26: 0000000000000000
> [ 62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0
> [ 62.063520] x23: 0000000000000000 x22: 00000006bfffffff
> [ 62.064540] x21: 00000000ffffffef x20: 00000000006c0000
> [ 62.065558] x19: 0000000000680000 x18: 0000000000000024
> [ 62.066566] x17: 0000000000000000 x16: 0000000000000000
> [ 62.067579] x15: ffffffffffffffff x14: ffff8005e412e890
> [ 62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000
> [ 62.069610] x11: ffff8005d6b10490 x10: 0000000000000040
> [ 62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890
> [ 62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00
> [ 62.072640] x5 : 0000000000000001 x4 : 0000000000000002
> [ 62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002
> [ 62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef
> [ 62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f)
> [ 62.076930] Call trace:
> [ 62.077411] add_memory_resource+0x1cc/0x1d8
> [ 62.078227] __add_memory+0x70/0xa8
> [ 62.078901] probe_store+0xa4/0xc8
> [ 62.079561] dev_attr_store+0x18/0x28
> [ 62.080270] sysfs_kf_write+0x40/0x58
> [ 62.080992] kernfs_fop_write+0xcc/0x1d8
> [ 62.081744] __vfs_write+0x18/0x40
> [ 62.082400] vfs_write+0xa4/0x1b0
> [ 62.083037] ksys_write+0x5c/0xc0
> [ 62.083681] __arm64_sys_write+0x18/0x20
> [ 62.084432] el0_svc_handler+0x88/0x100
> [ 62.085177] el0_svc+0x8/0xc
>
> Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the
> problem on arm64 as pfn_valid() behaves correctly and returns positive
> as memblock for the address range still exists. arch_remove_memory()
> removes applicable memory sections from zone with __remove_pages() and
> tears down kernel linear mapping. Removing memblock regions afterwards
> is safe because there is no other memblock (bootmem) allocator user that
> late. So nobody is going to allocate from the removed range just to blow
> up later. Also nobody should be using the bootmem allocated range else
> we wouldn't allow to remove it. So reordering is indeed safe.
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
Honestly, the issue is not clear from the changelog, largely
because I can't find the use of get_nid_for_pfn() being used
in memory hotunplug. I can see why using pfn_valid() after
memblock_free/remove is bad on the architecture.
I think the checks to pfn_valid() can be avoided from the
remove paths if we did the following
memblock_isolate_regions()
for each isolate_region {
memblock_free
memblock_remove
arch_memory_remove
# ensure that __remove_memory can avoid calling pfn_valid
}
Having said that, your patch is easier and if your assumption
about not using the memblocks is valid (after arch_memory_remove())
then might be the least resistant way forward
Balbir Singh.
> mm/memory_hotplug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..355c466e0621 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>
> /* remove memmap entry */
> firmware_map_remove(start, start + size, "System RAM");
> - memblock_free(start, size);
> - memblock_remove(start, size);
>
> /* remove memory block devices before removing memory */
> remove_memory_block_devices(start, size);
>
> arch_remove_memory(nid, start, size, NULL);
> + memblock_free(start, size);
> + memblock_remove(start, size);
> __release_memory_resource(start, size);
>
> try_offline_node(nid);
>
next prev parent reply other threads:[~2019-09-16 1:45 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-03 9:45 [PATCH V7 0/3] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-09-03 9:45 ` [PATCH V7 1/3] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove_memory() Anshuman Khandual
2019-09-04 8:16 ` David Hildenbrand
2019-09-05 4:27 ` Anshuman Khandual
2019-09-16 1:44 ` Balbir Singh [this message]
2019-09-18 9:28 ` Anshuman Khandual
2019-09-03 9:45 ` [PATCH V7 2/3] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Anshuman Khandual
2019-09-15 2:35 ` Balbir Singh
2019-09-18 9:12 ` Anshuman Khandual
2019-09-03 9:45 ` [PATCH V7 3/3] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-09-10 16:17 ` Catalin Marinas
2019-09-11 10:31 ` David Hildenbrand
2019-09-12 4:28 ` Anshuman Khandual
2019-09-12 8:37 ` Anshuman Khandual
2019-09-12 20:15 ` Catalin Marinas
2019-09-13 5:58 ` Anshuman Khandual
2019-09-13 10:09 ` Catalin Marinas
2019-09-17 4:36 ` Anshuman Khandual
2019-09-17 15:08 ` Catalin Marinas
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