From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Oscar Salvador <osalvador@suse.de>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Dan Williams <dan.j.williams@intel.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug_lock
Date: Tue, 24 Sep 2019 14:54:04 -0400 [thread overview]
Message-ID: <1569351244.5576.219.camel@lca.pw> (raw)
In-Reply-To: <20190924151147.GB23050@dhcp22.suse.cz>
On Tue, 2019-09-24 at 17:11 +0200, Michal Hocko wrote:
> On Tue 24-09-19 11:03:21, Qian Cai wrote:
> [...]
> > While at it, it might be a good time to rethink the whole locking over there, as
> > it right now read files under /sys/kernel/slab/ could trigger a possible
> > deadlock anyway.
> >
>
> [...]
> > [ 442.452090][ T5224] -> #0 (mem_hotplug_lock.rw_sem){++++}:
> > [ 442.459748][ T5224] validate_chain+0xd10/0x2bcc
> > [ 442.464883][ T5224] __lock_acquire+0x7f4/0xb8c
> > [ 442.469930][ T5224] lock_acquire+0x31c/0x360
> > [ 442.474803][ T5224] get_online_mems+0x54/0x150
> > [ 442.479850][ T5224] show_slab_objects+0x94/0x3a8
> > [ 442.485072][ T5224] total_objects_show+0x28/0x34
> > [ 442.490292][ T5224] slab_attr_show+0x38/0x54
> > [ 442.495166][ T5224] sysfs_kf_seq_show+0x198/0x2d4
> > [ 442.500473][ T5224] kernfs_seq_show+0xa4/0xcc
> > [ 442.505433][ T5224] seq_read+0x30c/0x8a8
> > [ 442.509958][ T5224] kernfs_fop_read+0xa8/0x314
> > [ 442.515007][ T5224] __vfs_read+0x88/0x20c
> > [ 442.519620][ T5224] vfs_read+0xd8/0x10c
> > [ 442.524060][ T5224] ksys_read+0xb0/0x120
> > [ 442.528586][ T5224] __arm64_sys_read+0x54/0x88
> > [ 442.533634][ T5224] el0_svc_handler+0x170/0x240
> > [ 442.538768][ T5224] el0_svc+0x8/0xc
>
> I believe the lock is not really needed here. We do not deallocated
> pgdat of a hotremoved node nor destroy the slab state because an
> existing slabs would prevent hotremove to continue in the first place.
>
> There are likely details to be checked of course but the lock just seems
> bogus.
Check 03afc0e25f7f ("slab: get_online_mems for
kmem_cache_{create,destroy,shrink}"). It actually talk about the races during
memory as well cpu hotplug, so it might even that cpu_hotplug_lock removal is
problematic?
next prev parent reply other threads:[~2019-09-24 18:54 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 14:36 [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug_lock David Hildenbrand
2019-09-24 14:48 ` Michal Hocko
2019-09-24 15:01 ` David Hildenbrand
2019-09-24 15:03 ` Qian Cai
2019-09-24 15:11 ` Michal Hocko
2019-09-24 18:54 ` Qian Cai [this message]
2019-09-25 7:02 ` David Hildenbrand
2019-09-25 16:01 ` Qian Cai
2019-09-25 17:48 ` Michal Hocko
2019-09-25 18:20 ` Qian Cai
2019-09-25 19:48 ` David Hildenbrand
2019-09-25 20:32 ` Qian Cai
2019-09-26 7:26 ` David Hildenbrand
2019-09-26 7:38 ` Michal Hocko
2019-09-26 7:26 ` Michal Hocko
2019-09-26 11:19 ` Qian Cai
2019-09-26 11:52 ` Michal Hocko
2019-09-26 13:02 ` Qian Cai
2019-09-26 13:14 ` David Hildenbrand
2019-09-25 10:03 ` Michal Hocko
2019-09-24 15:23 ` David Hildenbrand
2019-10-02 21:37 ` Qian Cai
2019-10-04 7:42 ` David Hildenbrand
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