From: "Rafael J. Wysocki" <rjw@rjwysocki.net> To: Michal Hocko <mhocko@kernel.org> Cc: Toshi Kani <toshi.kani@hp.com>, Jiri Kosina <jkosina@suse.cz>, joeyli <jlee@suse.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Date: Mon, 20 Mar 2017 22:24:42 +0100 [thread overview] Message-ID: <2735706.OR0SQDpVy6@aspire.rjw.lan> (raw) In-Reply-To: <20170320192938.GA11363@dhcp22.suse.cz> On Monday, March 20, 2017 03:29:39 PM Michal Hocko wrote: > Hi Rafael, Hi, > we have been chasing the following BUG() triggering during the memory > hotremove (remove_memory): > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > check_memblock_offlined_cb); > if (ret) > BUG(); > > and it took a while to learn that the issue is caused by > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > surprised to see such an option because at least for the memory hotplug > it cannot work at all. Memory hotplug fails when the memory is still > in use. Even if we do not BUG() here enforcing the hotplug operation > will lead to problematic behavior later like crash or a silent memory > corruption if the memory gets onlined back and reused by somebody else. > > I am wondering what was the motivation for introducing this behavior and > whether there is a way to disallow it for memory hotplug. Or maybe drop > it completely. What would break in such a case? Honestly, I don't remember from the top of my head and I haven't looked at that code for several months. I need some time to recall that. Thanks, Rafael
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From: "Rafael J. Wysocki" <rjw@rjwysocki.net> To: Michal Hocko <mhocko@kernel.org> Cc: Toshi Kani <toshi.kani@hp.com>, Jiri Kosina <jkosina@suse.cz>, joeyli <jlee@suse.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Date: Mon, 20 Mar 2017 22:24:42 +0100 [thread overview] Message-ID: <2735706.OR0SQDpVy6@aspire.rjw.lan> (raw) In-Reply-To: <20170320192938.GA11363@dhcp22.suse.cz> On Monday, March 20, 2017 03:29:39 PM Michal Hocko wrote: > Hi Rafael, Hi, > we have been chasing the following BUG() triggering during the memory > hotremove (remove_memory): > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > check_memblock_offlined_cb); > if (ret) > BUG(); > > and it took a while to learn that the issue is caused by > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > surprised to see such an option because at least for the memory hotplug > it cannot work at all. Memory hotplug fails when the memory is still > in use. Even if we do not BUG() here enforcing the hotplug operation > will lead to problematic behavior later like crash or a silent memory > corruption if the memory gets onlined back and reused by somebody else. > > I am wondering what was the motivation for introducing this behavior and > whether there is a way to disallow it for memory hotplug. Or maybe drop > it completely. What would break in such a case? Honestly, I don't remember from the top of my head and I haven't looked at that code for several months. I need some time to recall that. Thanks, Rafael -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-03-20 21:30 UTC|newest] Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-20 19:29 memory hotplug and force_remove Michal Hocko 2017-03-20 19:29 ` Michal Hocko 2017-03-20 21:24 ` Rafael J. Wysocki [this message] 2017-03-20 21:24 ` Rafael J. Wysocki 2017-03-21 16:13 ` joeyli 2017-03-21 16:13 ` joeyli 2017-03-28 7:58 ` Michal Hocko 2017-03-28 7:58 ` Michal Hocko 2017-03-28 15:22 ` Rafael J. Wysocki 2017-03-28 15:22 ` Rafael J. Wysocki 2017-03-30 8:47 ` Jiri Kosina 2017-03-30 8:47 ` Jiri Kosina 2017-03-30 16:20 ` Michal Hocko 2017-03-30 16:20 ` Michal Hocko 2017-03-30 16:57 ` joeyli 2017-03-30 16:57 ` joeyli 2017-03-30 16:57 ` joeyli 2017-03-30 20:15 ` Rafael J. Wysocki 2017-03-30 20:15 ` Rafael J. Wysocki 2017-03-30 20:15 ` Rafael J. Wysocki 2017-03-31 0:00 ` joeyli 2017-03-31 0:00 ` joeyli 2017-03-31 8:30 ` Michal Hocko 2017-03-31 8:30 ` Michal Hocko 2017-03-31 8:30 ` Michal Hocko 2017-03-31 10:49 ` joeyli 2017-03-31 10:49 ` joeyli 2017-03-31 10:49 ` joeyli 2017-03-31 10:55 ` Michal Hocko 2017-03-31 10:55 ` Michal Hocko 2017-03-31 10:55 ` Michal Hocko 2017-03-31 11:55 ` joeyli 2017-03-31 11:55 ` joeyli 2017-03-31 11:55 ` joeyli 2017-03-31 12:02 ` Michal Hocko 2017-03-31 12:02 ` Michal Hocko 2017-03-31 22:35 ` Rafael J. Wysocki 2017-03-31 22:35 ` Rafael J. Wysocki 2017-03-31 22:35 ` Rafael J. Wysocki
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