Re: [PATCH V5 1/3] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory()

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Mark Rutland <mark.rutland@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: mhocko@suse.com, mgorman@techsingularity.net, david@redhat.com,
	catalin.marinas@arm.com, will.deacon@arm.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	logang@deltatee.com, arunks@codeaurora.org, cai@lca.pw,
	ard.biesheuvel@arm.com, cpandya@codeaurora.org,
	james.morse@arm.com, akpm@linux-foundation.org,
	ira.weiny@intel.com, dan.j.williams@intel.com,
	linux-arm-kernel@lists.infradead.org, osalvador@suse.de
Subject: Re: [PATCH V5 1/3] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory()
Date: Fri, 7 Jun 2019 07:58:42 +0530	[thread overview]
Message-ID: <7d0538bb-aeef-f5f5-3371-db7b58dcb083@arm.com> (raw)
In-Reply-To: <20190530103709.GB56046@lakrids.cambridge.arm.com>

On 05/30/2019 04:07 PM, Mark Rutland wrote:
> On Wed, May 29, 2019 at 02:46:25PM +0530, Anshuman Khandual wrote:
>> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
>> 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 ]------------
>> [   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 arch_remove_memory() with memblock_[free|remove] 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.
>>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>

Hello Andrew,

Will it be possible for this particular patch of the series to be merged alone.
I am still reworking arm64 hot-remove parts as per the suggestions from Mark.
Just wondering if this patch which has been reviewed and acked for a while now
can be out of our way.

Also because this has some conflict with David's series which can be sorted out
earlier before arm64 hot-remove V6 series comes in.

From my previous response on this series last week, the following can resolve
the conflict with David's [v3, 09/11] patch.

C) Rebase (https://patchwork.kernel.org/patch/10962589/) [v3, 09/11]

	- hot-remove series moves arch_remove_memory() before memblock_[free|remove]()
	- So remove_memory_block_devices() should be moved before arch_remove_memory()
	  in it's new position   

It will be great if this patch can be merged alone.

- Anshuman

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