Messages in this thread | | | Date | Sat, 27 Mar 2021 18:53:08 +0100 | From | Oleg Nesterov <> | Subject | Re: [syzbot] possible deadlock in register_for_each_vma |
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Hi Hillf,
it seems that you already understand the problem ;) I don't.
Could you explain in details how double __register is possible ? and how it connects to this lockdep report?
On 03/27, Hillf Danton wrote: > > On Fri, 26 Mar 2021 03:29:19 > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 0d02ec6b Linux 5.12-rc4 > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1719e4aad00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=5adab0bdee099d7a > > dashboard link: https://syzkaller.appspot.com/bug?extid=b804f902bbb6bcf290cb > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+b804f902bbb6bcf290cb@syzkaller.appspotmail.com > > > > ====================================================== > > WARNING: possible circular locking dependency detected > > 5.12.0-rc4-syzkaller #0 Not tainted > > ------------------------------------------------------ > > syz-executor.3/23522 is trying to acquire lock: > > ffffffff8c03e530 (dup_mmap_sem){++++}-{0:0}, at: register_for_each_vma+0x2c/0xc10 kernel/events/uprobes.c:1040 > > > > but task is already holding lock: > > ffff8880624a8c90 (&uprobe->register_rwsem){+.+.}-{3:3}, at: __uprobe_register+0x531/0x850 kernel/events/uprobes.c:1177 > > > > which lock already depends on the new lock. > > > > > > the existing dependency chain (in reverse order) is: > > > > -> #3 (&uprobe->register_rwsem){+.+.}-{3:3}: > > down_write+0x92/0x150 kernel/locking/rwsem.c:1406 > > __uprobe_register+0x531/0x850 kernel/events/uprobes.c:1177 > > trace_uprobe_enable kernel/trace/trace_uprobe.c:1065 [inline] > > probe_event_enable+0x357/0xa00 kernel/trace/trace_uprobe.c:1134 > > trace_uprobe_register+0x443/0x880 kernel/trace/trace_uprobe.c:1461 > > perf_trace_event_reg kernel/trace/trace_event_perf.c:129 [inline] > > perf_trace_event_init+0x549/0xa20 kernel/trace/trace_event_perf.c:204 > > perf_uprobe_init+0x16f/0x210 kernel/trace/trace_event_perf.c:336 > > perf_uprobe_event_init+0xff/0x1c0 kernel/events/core.c:9754 > > perf_try_init_event+0x12a/0x560 kernel/events/core.c:11071 > > perf_init_event kernel/events/core.c:11123 [inline] > > perf_event_alloc.part.0+0xe3b/0x3960 kernel/events/core.c:11403 > > perf_event_alloc kernel/events/core.c:11785 [inline] > > __do_sys_perf_event_open+0x647/0x2e60 kernel/events/core.c:11883 > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > -> #2 (event_mutex){+.+.}-{3:3}: > > __mutex_lock_common kernel/locking/mutex.c:949 [inline] > > __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1096 > > perf_trace_destroy+0x23/0xf0 kernel/trace/trace_event_perf.c:241 > > _free_event+0x2ee/0x1380 kernel/events/core.c:4863 > > put_event kernel/events/core.c:4957 [inline] > > perf_mmap_close+0x572/0xe10 kernel/events/core.c:6002 > > remove_vma+0xae/0x170 mm/mmap.c:180 > > remove_vma_list mm/mmap.c:2653 [inline] > > __do_munmap+0x74f/0x11a0 mm/mmap.c:2909 > > do_munmap mm/mmap.c:2917 [inline] > > munmap_vma_range mm/mmap.c:598 [inline] > > mmap_region+0x85a/0x1730 mm/mmap.c:1750 > > do_mmap+0xcff/0x11d0 mm/mmap.c:1581 > > vm_mmap_pgoff+0x1b7/0x290 mm/util.c:519 > > ksys_mmap_pgoff+0x49c/0x620 mm/mmap.c:1632 > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > -> #1 (&mm->mmap_lock#2){++++}-{3:3}: > > down_write_killable+0x95/0x170 kernel/locking/rwsem.c:1417 > > mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline] > > dup_mmap kernel/fork.c:480 [inline] > > dup_mm+0x12e/0x1380 kernel/fork.c:1368 > > copy_mm kernel/fork.c:1424 [inline] > > copy_process+0x2b99/0x7150 kernel/fork.c:2107 > > kernel_clone+0xe7/0xab0 kernel/fork.c:2500 > > __do_sys_clone+0xc8/0x110 kernel/fork.c:2617 > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > -> #0 (dup_mmap_sem){++++}-{0:0}: > > check_prev_add kernel/locking/lockdep.c:2936 [inline] > > check_prevs_add kernel/locking/lockdep.c:3059 [inline] > > validate_chain kernel/locking/lockdep.c:3674 [inline] > > __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900 > > lock_acquire kernel/locking/lockdep.c:5510 [inline] > > lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475 > > percpu_down_write+0x95/0x440 kernel/locking/percpu-rwsem.c:217 > > register_for_each_vma+0x2c/0xc10 kernel/events/uprobes.c:1040 > > __uprobe_register+0x5c2/0x850 kernel/events/uprobes.c:1181 > > trace_uprobe_enable kernel/trace/trace_uprobe.c:1065 [inline] > > probe_event_enable+0x357/0xa00 kernel/trace/trace_uprobe.c:1134 > > trace_uprobe_register+0x443/0x880 kernel/trace/trace_uprobe.c:1461 > > perf_trace_event_reg kernel/trace/trace_event_perf.c:129 [inline] > > perf_trace_event_init+0x549/0xa20 kernel/trace/trace_event_perf.c:204 > > perf_uprobe_init+0x16f/0x210 kernel/trace/trace_event_perf.c:336 > > perf_uprobe_event_init+0xff/0x1c0 kernel/events/core.c:9754 > > perf_try_init_event+0x12a/0x560 kernel/events/core.c:11071 > > perf_init_event kernel/events/core.c:11123 [inline] > > perf_event_alloc.part.0+0xe3b/0x3960 kernel/events/core.c:11403 > > perf_event_alloc kernel/events/core.c:11785 [inline] > > __do_sys_perf_event_open+0x647/0x2e60 kernel/events/core.c:11883 > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > other info that might help us debug this: > > > > Chain exists of: > > dup_mmap_sem --> event_mutex --> &uprobe->register_rwsem > > > > Possible unsafe locking scenario: > > > > CPU0 CPU1 > > ---- ---- > > lock(&uprobe->register_rwsem); > > lock(event_mutex); > > lock(&uprobe->register_rwsem); > > lock(dup_mmap_sem); > > > > *** DEADLOCK *** > > > > 3 locks held by syz-executor.3/23522: > > #0: ffffffff8fe4fcd8 (&pmus_srcu){....}-{0:0}, at: perf_event_alloc.part.0+0xc8e/0x3960 kernel/events/core.c:11401 > > #1: ffffffff8bfe5688 (event_mutex){+.+.}-{3:3}, at: perf_uprobe_init+0x164/0x210 kernel/trace/trace_event_perf.c:335 > > #2: ffff8880624a8c90 (&uprobe->register_rwsem){+.+.}-{3:3}, at: __uprobe_register+0x531/0x850 kernel/events/uprobes.c:1177 > > > > stack backtrace: > > CPU: 0 PID: 23522 Comm: syz-executor.3 Not tainted 5.12.0-rc4-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > Call Trace: > > __dump_stack lib/dump_stack.c:79 [inline] > > dump_stack+0x141/0x1d7 lib/dump_stack.c:120 > > check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2127 > > check_prev_add kernel/locking/lockdep.c:2936 [inline] > > check_prevs_add kernel/locking/lockdep.c:3059 [inline] > > validate_chain kernel/locking/lockdep.c:3674 [inline] > > __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900 > > lock_acquire kernel/locking/lockdep.c:5510 [inline] > > lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475 > > percpu_down_write+0x95/0x440 kernel/locking/percpu-rwsem.c:217 > > register_for_each_vma+0x2c/0xc10 kernel/events/uprobes.c:1040 > > __uprobe_register+0x5c2/0x850 kernel/events/uprobes.c:1181 > > trace_uprobe_enable kernel/trace/trace_uprobe.c:1065 [inline] > > probe_event_enable+0x357/0xa00 kernel/trace/trace_uprobe.c:1134 > > trace_uprobe_register+0x443/0x880 kernel/trace/trace_uprobe.c:1461 > > perf_trace_event_reg kernel/trace/trace_event_perf.c:129 [inline] > > perf_trace_event_init+0x549/0xa20 kernel/trace/trace_event_perf.c:204 > > perf_uprobe_init+0x16f/0x210 kernel/trace/trace_event_perf.c:336 > > perf_uprobe_event_init+0xff/0x1c0 kernel/events/core.c:9754 > > perf_try_init_event+0x12a/0x560 kernel/events/core.c:11071 > > perf_init_event kernel/events/core.c:11123 [inline] > > perf_event_alloc.part.0+0xe3b/0x3960 kernel/events/core.c:11403 > > perf_event_alloc kernel/events/core.c:11785 [inline] > > __do_sys_perf_event_open+0x647/0x2e60 kernel/events/core.c:11883 > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Add a flag and check it to avoid double registering of uprobe. > > --- x/kernel/events/uprobes.c > +++ y/kernel/events/uprobes.c > @@ -51,6 +51,7 @@ DEFINE_STATIC_PERCPU_RWSEM(dup_mmap_sem) > > /* Have a copy of original instruction */ > #define UPROBE_COPY_INSN 0 > +#define UPROBE_REGISTERING 1 > > struct uprobe { > struct rb_node rb_node; /* node in the rb tree */ > @@ -1170,6 +1171,9 @@ static int __uprobe_register(struct inod > if (IS_ERR(uprobe)) > return PTR_ERR(uprobe); > > + /* no point to register twice at the cost of deadlock */ > + if (test_and_set_bit(UPROBE_REGISTERING, &uprobe->flags)) > + return 0; > /* > * We can race with uprobe_unregister()->delete_uprobe(). > * Check uprobe_is_active() and retry if it is false. > @@ -1183,6 +1187,7 @@ static int __uprobe_register(struct inod > __uprobe_unregister(uprobe, uc); > } > up_write(&uprobe->register_rwsem); > + clear_bit(UPROBE_REGISTERING, &uprobe->flags); > put_uprobe(uprobe); > > if (unlikely(ret == -EAGAIN)) >
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