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Date: Sat, 27 Mar 2021 18:53:08 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+b804f902bbb6bcf290cb@...kaller.appspotmail.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
peterz@...radead.org, Greg KH <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] possible deadlock in register_for_each_vma
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@...kaller.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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