From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup Date: Fri, 3 Jun 2016 12:05:05 +0200 Message-ID: <20160603100505.GE20676@dhcp22.suse.cz> References: <20160601131122.7dbb0a65@canb.auug.org.au> <20160602014835.GA635@swordfish> <20160602092113.GH1995@dhcp22.suse.cz> <20160603071551.GA453@swordfish> <20160603072536.GB20676@dhcp22.suse.cz> <20160603084347.GA502@swordfish> <20160603095549.GD20676@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160603095549.GD20676@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Sergey Senozhatsky Cc: Andrew Morton , Vlastimil Babka , "Kirill A. Shutemov" , Stephen Rothwell , linux-mm@kvack.org, linux-next@vger.kernel.org, linux-kernel@vger.kernel.org, Andrea Arcangeli List-Id: linux-next.vger.kernel.org On Fri 03-06-16 11:55:49, Michal Hocko wrote: > On Fri 03-06-16 17:43:47, Sergey Senozhatsky wrote: > > On (06/03/16 09:25), Michal Hocko wrote: > > > > it's quite hard to trigger the bug (somehow), so I can't > > > > follow up with more information as of now. > > > > either I did something very silly fixing up the patch, or the > > patch may be causing general protection faults on my system. > > > > RIP collect_mm_slot() + 0x42/0x84 > > khugepaged > > So is this really collect_mm_slot called directly from khugepaged or is > some inlining going on there? > > > prepare_to_wait_event > > maybe_pmd_mkwrite > > kthread > > _raw_sin_unlock_irq > > ret_from_fork > > kthread_create_on_node > > > > collect_mm_slot() + 0x42/0x84 is > > I guess that the problem is that I have missed that __khugepaged_exit > doesn't clear the cached khugepaged_scan.mm_slot. Does the following on > top fixes that? That wouldn't be sufficient after a closer look. We need to do the same from khugepaged_scan_mm_slot when atomic_inc_not_zero fails. So I guess it would be better to stick it into collect_mm_slot. Thanks for your testing! --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 6574c62ca4a3..0432581fb87c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2011,6 +2011,9 @@ static void collect_mm_slot(struct mm_slot *mm_slot) /* khugepaged_mm_lock actually not necessary for the below */ free_mm_slot(mm_slot); mmdrop(mm); + + if (khugepaged_scan.mm_slot == mm_slot) + khugepaged_scan.mm_slot = NULL; } } -- Michal Hocko SUSE Labs