Thank you for all your comments.
Thanks, Kyungtae Kim On Wed, Nov 14, 2018 at 11:05 AM Paul E. McKenney <paul...@linux.ibm.com> wrote: > > On Wed, Nov 14, 2018 at 04:31:11PM +0100, Alexander Potapenko wrote: > > On Wed, Nov 14, 2018 at 4:09 PM Paul E. McKenney <paul...@linux.ibm.com> > > wrote: > > > > > > On Wed, Nov 14, 2018 at 04:03:33AM -0500, Kyungtae Kim wrote: > > > > We report two crashes in v4.19-rc8 (4.20-rc1 as well, I guess): > > > > (Unfortunately, there is no repro for those.) > > > > > > > > The two crashes seem to share the same issue. > > > > In both cases, (uninitialized) memory access violation occurs > > > > when "rdp->cblist" is about to be accessed > > > > (kernel/rcu/tree.c:2838,1728). > > > > I guess those are freed before the use, but I still haven't figured > > > > out the reason why. > > > > I'm looking forward to some help. > > > > First of all, I'd avoid reporting KMSAN bugs without clear reproducers. > > The tool is still in beta and may still give false positives due to > > either missed initialization or rare memory corruptions. > > OK, I will set this aside, then, thank you! > > Thanx, Paul > > > > You lost me on this one. In both cases, rdp references a per-CPU > > > variable that is implicitly initialized to all zeroes, due to being > > > (sort of) a C-language global. > > > > > > If a callback is queued early, then the following lines in __call_rcu() > > > will make an honest list of that field because of the : > > > > > > if (rcu_segcblist_empty(&rdp->cblist)) > > > rcu_segcblist_init(&rdp->cblist); > > > > > > Otherwise, when rcu_init() is invoked during early boot, we have this > > > in rcu_init_percpu_data(), which is called from rcutree_prepare_cpu() > > > which is called from rcu_init(), which is called from start_kernel(): > > > > > > if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */ > > > !init_nocb_callback_list(rdp)) > > > rcu_segcblist_init(&rdp->cblist); /* Re-enable > > > callbacks. */ > > > > > > So either init_nocb_callback_list() initializes the alternative callback > > > lists for a no-CBs CPU or rcu_segcblist_init() again makes an honest > > > list of that field. > > > > > > My guess is that your tool is missing the > > > > > > rdp = this_cpu_ptr(rsp->rda); > > > > > > in the __call_rcu() case, and also missing the > > > > > > struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); > > > > > > Note that the ->rda field is explicitly compile-time initialized to > > > the base address of the per-CPU variable, which is rcu_preempt_data, > > > rcu_bh_data, or rcu_sched_data, depending on which RCU flavor is at hand. > > > (In v4.20-rc1, these are all merged into a single flavor to rule them > > > all.) > > > > > > Alternatively, your tool might be missing the implicit initialization > > > of per-CPU variables. > > This used to be fine, but after rebasing to v4.20-rc2 I also started > > seeing strange reports on per-CPU variables. Taking a look. > > > Or maybe I am missing something. If so, please let me know what it is. > > > > > > Thanx, Paul > > > > > > > Crash log 1 > > > > ========================================= > > > > BUG: KMSAN: uninit-value in __rcu_process_callbacks > > > > kernel/rcu/tree.c:2838 [inline] > > > > BUG: KMSAN: uninit-value in rcu_process_callbacks+0x5ac/0x1cb0 > > > > kernel/rcu/tree.c:2864 > > > > CPU: 0 PID: 20 Comm: kauditd Not tainted 4.19.0-rc8+ #18 > > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs > > > > 01/01/2011 > > > > Call Trace: > > > > <IRQ> > > > > __dump_stack lib/dump_stack.c:77 [inline] > > > > dump_stack+0x305/0x460 lib/dump_stack.c:113 > > > > kmsan_report+0x1a2/0x2e0 mm/kmsan/kmsan.c:917 > > > > __msan_warning+0x7d/0xe0 mm/kmsan/kmsan_instr.c:500 > > > > __rcu_process_callbacks kernel/rcu/tree.c:2838 [inline] > > > > rcu_process_callbacks+0x5ac/0x1cb0 kernel/rcu/tree.c:2864 > > > > __do_softirq+0x5ff/0xa55 kernel/softirq.c:292 > > > > invoke_softirq kernel/softirq.c:373 [inline] > > > > irq_exit+0x22d/0x270 kernel/softirq.c:414 > > > > exiting_irq+0xe/0x10 arch/x86/include/asm/apic.h:536 > > > > smp_apic_timer_interrupt+0x64/0x90 arch/x86/kernel/apic/apic.c:1059 > > > > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:869 > > > > </IRQ> > > > > RIP: 0010:finish_lock_switch+0x2b/0x40 kernel/sched/core.c:2578 > > > > Code: 48 89 e5 53 48 89 fb e8 e3 43 9a 00 8b b8 88 0c 00 00 48 8b 00 > > > > 48 85 c0 75 12 48 89 df e8 7d 38 9a 00 c6 00 00 c6 03 00 fb 5b <5d> c3 > > > > e8 de 42 9a 00 eb e7 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 > > > > RSP: 0018:ffff88010622fca0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13 > > > > RAX: ffff8801105bcc40 RBX: ffff8801061554c0 RCX: ffff8801105bdc40 > > > > RDX: ffff8801105bdc40 RSI: aaaaaaaaaaaab000 RDI: ffffea00077ec560 > > > > RBP: ffff88010622fca0 R08: ffffffff7fffffff R09: 0000000000000002 > > > > R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800751cb880 > > > > R13: 0000000000000000 R14: ffff880106155db8 R15: ffff88013fcb9c40 > > > > finish_task_switch+0xe3/0x270 kernel/sched/core.c:2679 > > > > context_switch kernel/sched/core.c:2832 [inline] > > > > __schedule+0x78f/0x8f0 kernel/sched/core.c:3479 > > > > schedule+0x1cc/0x300 kernel/sched/core.c:3523 > > > > kauditd_thread+0xc64/0xee0 kernel/audit.c:889 > > > > kthread+0x5b1/0x5f0 kernel/kthread.c:247 > > > > ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:416 > > > > > > > > Uninit was created at: > > > > kmsan_save_stack_with_flags mm/kmsan/kmsan.c:255 [inline] > > > > kmsan_internal_alloc_meta_for_pages+0x157/0x730 mm/kmsan/kmsan.c:693 > > > > kmsan_alloc_page+0x80/0xe0 mm/kmsan/kmsan_hooks.c:320 > > > > __alloc_pages_nodemask+0x128c/0x69b0 mm/page_alloc.c:4416 > > > > alloc_pages_current+0x51f/0x760 mm/mempolicy.c:2093 > > > > alloc_pages include/linux/gfp.h:511 [inline] > > > > alloc_slab_page mm/slub.c:1459 [inline] > > > > allocate_slab mm/slub.c:1604 [inline] > > > > new_slab+0x552/0x1f30 mm/slub.c:1675 > > > > new_slab_objects mm/slub.c:2438 [inline] > > > > ___slab_alloc+0x1414/0x1dd0 mm/slub.c:2590 > > > > __slab_alloc mm/slub.c:2630 [inline] > > > > slab_alloc_node mm/slub.c:2693 [inline] > > > > slab_alloc mm/slub.c:2735 [inline] > > > > kmem_cache_alloc+0xc9b/0xda0 mm/slub.c:2740 > > > > kmem_cache_zalloc include/linux/slab.h:697 [inline] > > > > avc_alloc_node+0x109/0xb90 security/selinux/avc.c:572 > > > > avc_update_node+0x172/0x1ee0 security/selinux/avc.c:859 > > > > avc_denied+0x312/0x360 security/selinux/avc.c:1024 > > > > avc_has_perm_noaudit+0x733/0x770 security/selinux/avc.c:1155 > > > > avc_has_perm+0x172/0x480 security/selinux/avc.c:1184 > > > > sock_has_perm security/selinux/hooks.c:4539 [inline] > > > > selinux_socket_sendmsg+0x297/0x360 security/selinux/hooks.c:4875 > > > > security_socket_sendmsg+0x127/0x200 security/security.c:1410 > > > > sock_sendmsg net/socket.c:628 [inline] > > > > ___sys_sendmsg+0xd5f/0x1290 net/socket.c:2116 > > > > __sys_sendmsg net/socket.c:2154 [inline] > > > > __do_sys_sendmsg net/socket.c:2163 [inline] > > > > __se_sys_sendmsg+0x307/0x460 net/socket.c:2161 > > > > __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2161 > > > > do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291 > > > > entry_SYSCALL_64_after_hwframe+0x63/0xe7 > > > > ========================================================= > > > > > > > > Crash log 2 > > > > ========================================================= > > > > BUG: KMSAN: uninit-value in rcu_accelerate_cbs+0x821/0x990 > > > > kernel/rcu/tree.c:1728 > > > > CPU: 0 PID: 10 Comm: rcu_sched Not tainted 4.19.0-rc8+ #18 > > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs > > > > 01/01/2011 > > > > Call Trace: > > > > __dump_stack lib/dump_stack.c:77 [inline] > > > > dump_stack+0x305/0x460 lib/dump_stack.c:113 > > > > kmsan_report+0x1a2/0x2e0 mm/kmsan/kmsan.c:917 > > > > __msan_warning+0x7d/0xe0 mm/kmsan/kmsan_instr.c:500 > > > > rcu_accelerate_cbs+0x821/0x990 kernel/rcu/tree.c:1728 > > > > __note_gp_changes+0x2ac/0x9e0 kernel/rcu/tree.c:1807 > > > > rcu_gp_cleanup kernel/rcu/tree.c:2109 [inline] > > > > rcu_gp_kthread+0x3019/0x3990 kernel/rcu/tree.c:2236 > > > > kthread+0x5b1/0x5f0 kernel/kthread.c:247 > > > > ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:416 > > > > > > > > Uninit was created at: > > > > kmsan_save_stack_with_flags mm/kmsan/kmsan.c:255 [inline] > > > > kmsan_internal_alloc_meta_for_pages+0x157/0x730 mm/kmsan/kmsan.c:693 > > > > kmsan_alloc_page+0x80/0xe0 mm/kmsan/kmsan_hooks.c:320 > > > > __alloc_pages_nodemask+0x128c/0x69b0 mm/page_alloc.c:4416 > > > > alloc_pages_current+0x51f/0x760 mm/mempolicy.c:2093 > > > > alloc_pages include/linux/gfp.h:511 [inline] > > > > alloc_slab_page mm/slub.c:1459 [inline] > > > > allocate_slab mm/slub.c:1604 [inline] > > > > new_slab+0x552/0x1f30 mm/slub.c:1675 > > > > new_slab_objects mm/slub.c:2438 [inline] > > > > ___slab_alloc+0x1414/0x1dd0 mm/slub.c:2590 > > > > __slab_alloc mm/slub.c:2630 [inline] > > > > slab_alloc_node mm/slub.c:2693 [inline] > > > > slab_alloc mm/slub.c:2735 [inline] > > > > kmem_cache_alloc+0xc9b/0xda0 mm/slub.c:2740 > > > > kmem_cache_zalloc include/linux/slab.h:697 [inline] > > > > avc_alloc_node+0x109/0xb90 security/selinux/avc.c:572 > > > > avc_insert security/selinux/avc.c:696 [inline] > > > > avc_compute_av+0x31e/0x1050 security/selinux/avc.c:1008 > > > > avc_has_perm_noaudit+0x516/0x770 security/selinux/avc.c:1149 > > > > avc_has_perm+0x172/0x480 security/selinux/avc.c:1184 > > > > selinux_socket_create+0x248/0x3c0 security/selinux/hooks.c:4560 > > > > security_socket_create+0x146/0x210 security/security.c:1372 > > > > __sock_create+0x26b/0xf30 net/socket.c:1232 > > > > sock_create net/socket.c:1317 [inline] > > > > __sys_socket+0x180/0x670 net/socket.c:1347 > > > > __do_sys_socket net/socket.c:1356 [inline] > > > > __se_sys_socket+0x8d/0xb0 net/socket.c:1354 > > > > __x64_sys_socket+0x4a/0x70 net/socket.c:1354 > > > > do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291 > > > > entry_SYSCALL_64_after_hwframe+0x63/0xe7 > > > > ========================================================= > > > > > > > > Thanks, > > > > Kyungtae Kim > > > > > > > > > > -- > > > You received this message because you are subscribed to the Google Groups > > > "syzkaller" group. > > > To unsubscribe from this group and stop receiving emails from it, send an > > > email to syzkaller+unsubscr...@googlegroups.com. > > > For more options, visit https://groups.google.com/d/optout. > > > > > > > > -- > > Alexander Potapenko > > Software Engineer > > > > Google Germany GmbH > > Erika-Mann-Straße, 33 > > 80636 München > > > > Geschäftsführer: Paul Manicle, Halimah DeLaine Prado > > Registergericht und -nummer: Hamburg, HRB 86891 > > Sitz der Gesellschaft: Hamburg > > >
