From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: [memory sharing] bug on get_page_and_type Date: Tue, 1 Feb 2011 14:28:16 +0000 Message-ID: <20110201142816.GE20638@whitby.uk.xensource.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: George Dunlap Cc: MaoXiaoyun , xen devel , "juihaochiang@gmail.com" List-Id: xen-devel@lists.xenproject.org At 12:47 +0000 on 31 Jan (1296478031), George Dunlap wrote: > At first glance, it does look like a race, of the type that would > normally be done by grabbing the p2m lock. I'd have to take a closer > look to be sure, but I won't be able to for at least another day or > two. Maybe Tim can comment. Yes, this is a race; it would be fixed by getting rid of the shr_lock and using the p2m lock to cover page-sahring operations, which I think is a good idea anyway. I think I'll have time to look at the locking properly some time this month. Of course, I've been wrong before. :) Tim. > 2011/1/31 MaoXiaoyun : > > Hi Georage: > > > > Thanks for your help, I think I really need to learn hg a bit. > > Well, when looking into memory sharing code, a confusion > > really brother me a lot. > > I think maybe you can enlighten me. > > > > There has been *check action code* do like below steps > > 1) Use gfn_to_mfn to get p2m_type_t p2mt > > 2) check the type of p2mt, > > 3) do some stuffes base if check on step 2 is failed > > > > While when *nominate page* to be shared, it does these follow steps > > a) check page whether can be shared > > b) call page_make_sharable to make sharable > > c) if 2) is success, call p2m_change_type to update page type > > p2m_ram_shared > > > > My confusion is if *nominate page* code reach step b, and before it go > > to step c > > *check action code* reach its step2, it will find page type is > > not p2m_ram_shared > > and go to step3. And later "nominate page" code go to step (c) > > > > Take xen/common/memory.c for example, > > line 179 is much like step 2, it will goto 196 to clear the _PGC_allocated > > flag > > if check failed, so it might indicates, *nominate page* code change the page > > type > > into p2m_ram_shared, but the page actually has alreay been freed. > > > > Am I right? > > > > > > 155 int guest_remove_page(struct domain *d, unsigned long gmfn) > > 156 { > > 157 struct page_info *page; > > 158 #ifdef CONFIG_X86 > > 159 p2m_type_t p2mt; > > 160 #endif > > 161 unsigned long mfn; > > 162 > > 163 #ifdef CONFIG_X86 > > 164 mfn = mfn_x(gfn_to_mfn(d, gmfn, &p2mt)); > > 165 #else > > 166 mfn = gmfn_to_mfn(d, gmfn); > > 167 #endif > > 168 if ( unlikely(!mfn_valid(mfn)) ) > > 169 { > > 170 gdprintk(XENLOG_INFO, "Domain %u page number %lx invalid\n", > > 171 d->domain_id, gmfn); > > 172 return 0; > > 173 } > > 174 > > 175  ; page = mfn_to_page(mfn); > > 176 #ifdef CONFIG_X86 > > 177 /* If gmfn is shared, just drop the guest reference (which may or > > may not > > 178 * free the page) */ > > 179 if(p2m_is_shared(p2mt)) > > 180 { > > 181 put_page_and_type(page); > > 182 guest_physmap_remove_page(d, gmfn, mfn, 0); > > 183 return 1; > > 184 } > > 185 > > 186 #endif /* CONFIG_X86 */ > > 187 if ( unlikely(!get_page(page, d)) ) > > 188 { > > 189 gdprintk(XENLOG_INFO, "Bad page free for domain %u\n", > > d->domain_id); > > 190 return 0; > > 189 gdprintk(XENLOG_INFO, "Bad page free for domain %u\n", > > d->domain_id); > > 190 return 0; > > 191 } > > 192 > > 193 if ( test_and_clear_bit(_PGT_pinned, &page->u.inuse.type_info) ) > > 194 put_page_and_type(page); > > 195 > > 196 if ( test_and_clear_bit(_PGC_allocated, &page->count_info) ) > > 197 put_page(page); > > 198 > > 199 guest_physmap_remove_page(d, gmfn, mfn, 0); > > 200 > > 201 put_page(page); > > 202 > > 203 return 1; > > 204 } > > > >> Date: Mon, 31 Jan 2011 10:49:37 +0000 > >> Subject: Re: [Xen-devel] [memory sharing] bug on get_page_and_type > >> From: George.Dunlap@eu.citrix.com > >> To: tinnycloud@hotmail.com > >> CC: xen-devel@lists.xensource.com; tim.deegan@citrix.com; > >> juihaochiang@gmail.com > >> > >> Xiaoyun, > >> > >> Thanks for all of your work getting page sharing working. When > >> submitting patches, please break them down into individual chunks, > >> each of which does one thing. Each patch should also include a > >> comment saying what the patch does and why, and a Signed-off-by line > >> indicating that you certify that the copyright holder (possibly you) > >> is placing the code under the GPL. > >> > >> Using mercurial queues: > >> http://mercurial.selenic.com/wiki/MqExtension > >> and the mercurial patchbomb extension: > >> http://mercurial.selenic.com/wiki/PatchbombExtension > >> are particularly handy for this process. > > &g t; > >> Quick comment: The ept-locking part of the patch is going to be > >> NACK-ed, as it will cause circular locking dependencies with the > >> hap_lock. c/s 22526:7a5ee380 has an explanation of the circular > >> dependency, and a fix which doesn't introduce a circular dependency. > >> (It may need to be adapted a bit to apply to 4.0-testing) > >> > >> -George > >> > >> On Mon, Jan 31, 2011 at 10:13 AM, tinnycloud > >> wrote: > >> > Hi: > >> > > >> > > >> > Attached is the whole patch suit for latest xen-4.0-testing,changeset > >> > 21443, > >> > > >> > It comes from George, Tim and JuiHao, also, has some extra debug info. > >> > > >> > > >> > > >> > On most occasion, memory sharing works fine, but still exists a bug. > >> > > >> > I?ve been tracing this problem for a while. > >> > > >> > &nbs p; There is a bug on get_page_and_type() in > >> > mem_sharing_share_pages() > >> > > >> > > >> > > >> > > >> > --------------------------------------------mem_sharing_share_pages()----------------------- > >> > > >> > 789 if(!get_page_and_type(spage, dom_cow, PGT_shared_page)){ > >> > > >> > 790 mem_sharing_debug_gfn(cd, gfn->gfn); > >> > > >> > 791 mem_sharing_debug_gfn(sd, sgfn->gfn); > >> > > >> > 792 printk("c->dying %d s->dying %d spage %p se->mfn %lx\n", > >> > cd->is_dying, sd->is_dying, spage, se->mfn); > >> > > >> > 793 printk("Debug page: MFN=%lx is ci=%lx, ti=%lx, > >> > owner_id=%d\n", > >> > > >> > 794 mfn_x(page_to_mfn(spage)), > >> > > >> > 795 spage->count_info, > >> > > >> > 796 spage->u.inuse.type_info, > >> > > >> > 797 page_get_owner(spage)->domain_id); > >> > > >> > 798 BUG(); > >> > > >> > 799 } > >> > > >> > > >> > > >> > > >> > > >> > Below painc log contains the debug info from line 790-798. > >> > > >> > We saw that 180000000000000 which is PGC_state_free, > >> > > >> > So it looks like a shared page has been freed unexpectly. > >> > > >> > > >> > > >> > > >> > > >> > (XEN) teardown 64 > >> > > >> > (XEN) teardown 66 > >> > > >> > blktap_sysfs_destroy > >> > > >> > blktap_sysfs_create: adding attributes for dev ffff880109d0c200 > >> > > >> > blktap_sysfs_destroy > >> > > >> > __ratelimit: 1 callbacks suppressed > >> > > >> > blktap_sysfs_destroy > >> > > >> > (XEN) Debug for domain=83, gfn=1e8dc, Debug page: MFN=1306dc is > >> > ci=8000000000000005, ti=8400000000000001, owner_id=32755 > >> > > >> > (XEN) Debug for domain=79, gfn=1dc95, Invalid MFN=ffffffffffffffff > >> > > >> > (XEN) c->dying 0 s->dying 0 spage ffff82f60a0f12a0 se->mfn 507895 > >> > > >> > (XEN) Debug page: MFN=507895 is ci= 180000000000000, > >> > ti=8400000000000001, > >> > owner_id=32755 > >> > > >> > (XEN) Xen BUG at mem_sharing.c:798 > >> > > >> > (XEN) ----[ Xen-4.0.2-rc2-pre x86_64 debug=n Not tainted ]---- > >> > > >> > (XEN) CPU: 0 > >> > > >> > (XEN) RIP: e008:[] > >> > mem_sharing_share_pages+0x5b0/0x5d0 > >> > > >> > (XEN) RFLAGS: 0000000000010286 CONTEXT: hypervisor > >> > > >> > (XEN) rax: 0000000000000000 rbx: ffff83044ef76000 rcx: > >> > 0000000000000092 > >> > > >> > (XEN) rdx: 000000000000000a rsi: 000000000000000a rdi: > >> > ffff82c4802237c4 > >> > > >> > (XEN) rbp: ffff83030d99e310 rsp: ffff82c48035fc48 r8: > >> > 0000000000000001 > >> > > >> > (XEN) r9: 0000000000000001 r10: 00000000fffffff8 r11: > >> > 0000000000000005 > >> > > >> > (XEN) r12: ffff83050b558000 r13: ffff830626ec5740 r14: > >> > 0000000000347967 > >> > > >> > (XEN) r15: ffff83030d99e068 cr0: 0000000080050033 cr4: > >> > 00000000000026f0 > >> > > >> > (XEN) cr3: 000000010e642000 cr2: 00002abdc4809000 > >> > > >> > (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e010 cs: e008 > >> > > >> > (XEN) Xen stack trace from rsp=ffff82c48035fc48: > >> > > >> > (XEN) 000000000001e8dc ffff83030d99e068 0000000000507895 > >> > ffff83030d99e050 > >> > > >> > (XEN) ffff82f60a0f12a0 ffff82f60260db80 ffff83030d99e300 > >> > ffff830626afbbd0 > >> > > >> > (XEN)&nb sp; 0000000080372980 ffff82c48035fe38 ffff83023febe000 > >> > 00000000008f7000 > >> > > >> > (XEN) 0000000000305000 0000000000000006 0000000000000006 > >> > ffff82c4801c44a4 > >> > > >> > (XEN) ffff82c480258188 ffff82c48011cb89 000000000001e8dc > >> > fffffffffffffff3 > >> > > >> > (XEN) ffff82c48035fe28 ffff82c480148503 000003d932971281 > >> > 0000000000000080 > >> > > >> > (XEN) 000003d9329611d6 ffff82c48018aedf ffff82c4803903a8 > >> > ffff82c48035fd38 > >> > > >> > (XEN) ffff82c480390380 ffff82c48035fe28 0000000000000002 > >> > 0000000000000000 > >> > > >> > (XEN) 0000000000000002 0000000000000000 ffff83023febe000 > >> > ffff83023ff80080 > >> > > >> > (XEN) ffff82c48035fe58 0000000000000000 ffff82c48022ca80 > >> > 0000000000000000 > >> > > >> > (XEN) 0000000000000002 ffff82c48018a 452 0000000000000000 > >> > ffff82c48016f6bb > >> > > >> > (XEN) ffff82c48035fe58 ffff82c4801538ea 000000023ab79067 > >> > fffffffffffffff3 > >> > > >> > (XEN) ffff82c48035fe28 00000000008f7000 0000000000305000 > >> > 0000000000000006 > >> > > >> > (XEN) 0000000000000006 ffff82c4801042b3 0000000000000000 > >> > ffff82c48010d2a5 > >> > > >> > (XEN) ffff830477fb51e8 0000000000000000 00007ff000000200 > >> > ffff8300bf76e000 > >> > > >> > (XEN) 0000000600000039 0000000000000000 00007fc09d744003 > >> > 0000000000325258 > >> > > >> > (XEN) 0000000000347967 ffffffffff600429 000000004d463b17 > >> > 0000000000062fe2 > >> > > >> > (XEN) 0000000000000000 00007fc09d744070 00007fc09d744000 > >> > 00007fffcfec0d20 > >> > > >> > (XEN) 00007fc09d744078 0000000000430fd8 00007fffcfec0d88 > >> > 00000000019f1ca8 > >> > > >> > (XEN) 0000f05c00000000 00007fc09f4c2718 0000000000000000 > >> > 0000000000000246 > >> > > >> > (XEN) Xen call trace: > >> > > >> > (XEN) [] mem_sharing_share_pages+0x5b0/0x5d0 > >> > > >> > (XEN) [] mem_sharing_domctl+0xe4/0x130 > >> > > >> > (XEN) [] cpumask_raise_softirq+0x89/0xa0 > >> > > >> > (XEN) [] arch_do_domctl+0x14f3/0x22d0 > >> > > >> > (XEN) [] handle_hpet_broadcast+0x16f/0x1d0 > >> > > >> > (XEN) [] hpet_legacy_irq_tick+0x42/0x50 > >> > > >> > (XEN) [] timer_interrupt+0xb/0x130 > >> > > >> > (XEN) [ ] ack_edge_ioapic_irq+0x2a/0x70 > >> > > >> > (XEN) [] do_domctl+0x163/0xfe0 > >> > > >> > (XEN) [] do_grant_table_op+0x75/0x1ad0 > >> > > >> > (XEN) [] syscall_enter+0xa9/0xae > >> > > >> > (XEN) > >> > > >> > (XEN) > >> > > >> > (XEN) **************************************** > >> > > >> > (XEN) Panic on CPU 0: > >> > > >> > (XEN) Xen BUG at mem_sharing.c:798 > >> > > >> > (XEN) **************************************** > >> > > >> > (XEN) > >> > > >> > (XEN) Manual reset required ('noreboot' specified) > >> > > >> > > >> > > >> > _______________________________________________ > >> > Xen-devel mailing list > >> > Xen-devel@lists.xensource.com > >> > http://lists.xensource.com/xen- devel > >> > > >> > > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@lists.xensource.com > > http://lists.xensource.com/xen-devel > > > > -- Tim Deegan Principal Software Engineer, Xen Platform Team Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)