[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [memory sharing] bug on get_page_and_type
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. -George 2011/1/31 MaoXiaoyun <tinnycloud@xxxxxxxxxxx>: > 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@xxxxxxxxxxxxx >> To: tinnycloud@xxxxxxxxxxx >> CC: xen-devel@xxxxxxxxxxxxxxxxxxx; tim.deegan@xxxxxxxxxx; >> juihaochiang@xxxxxxxxx >> >> 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 <tinnycloud@xxxxxxxxxxx> >> 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:[<ffff82c4801c3760>] >> > 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) [<ffff82c4801c3760>] mem_sharing_share_pages+0x5b0/0x5d0 >> > >> > (XEN) [<ffff82c4801c44a4>] mem_sharing_domctl+0xe4/0x130 >> > >> > (XEN) [<ffff82c48011cb89>] cpumask_raise_softirq+0x89/0xa0 >> > >> > (XEN) [<ffff82c480148503>] arch_do_domctl+0x14f3/0x22d0 >> > >> > (XEN) [<ffff82c48018aedf>] handle_hpet_broadcast+0x16f/0x1d0 >> > >> > (XEN) [<ffff82c48018a452>] hpet_legacy_irq_tick+0x42/0x50 >> > >> > (XEN) [<ffff82c48016f6bb>] timer_interrupt+0xb/0x130 >> > >> > (XEN) [<ffff82c4801538ea> ] ack_edge_ioapic_irq+0x2a/0x70 >> > >> > (XEN) [<ffff82c4801042b3>] do_domctl+0x163/0xfe0 >> > >> > (XEN) [<ffff82c48010d2a5>] do_grant_table_op+0x75/0x1ad0 >> > >> > (XEN) [<ffff82c4801e7169>] 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@xxxxxxxxxxxxxxxxxxx >> > http://lists.xensource.com/xen- devel >> > >> > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel > > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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