Sasha Levin <sasha.levin@xxxxxxxxxx> writes:
> Hi all,
>
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following spew:
Weird. I took a quick look and I don't see any changes in d_walk that
in Al's tree or in Linus's kernel for years.
Has read_seqbegin_or_lock changed somewhere?
>From a quick reading of the code it simply isn't possible for d_walk to
take the lock twice short of memory corruption. And the fact that the
code has not changed in years seems to suggest it isn't the obvious
cause of d_walk talking the rename_lock twice.
Eric
> [ 6172.870045] =============================================
> [ 6172.870045] [ INFO: possible recursive locking detected ]
> [ 6172.870045] 3.18.0-rc1-next-20141023-sasha-00036-g4dcabd5 #1415 Not tainted
> [ 6172.870045] ---------------------------------------------
> [ 6172.870045] trinity-c55/12752 is trying to acquire lock:
> [ 6172.870045] (rename_lock){+.+...}, at: d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045]
> [ 6172.870045] but task is already holding lock:
> [ 6172.870045] (rename_lock){+.+...}, at: d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045]
> [ 6172.870045] other info that might help us debug this:
> [ 6172.900904] FAULT_INJECTION: forcing a failure
> [ 6172.870045] Possible unsafe locking scenario:
> [ 6172.870045]
> [ 6172.870045] CPU0
> [ 6172.870045] ----
> [ 6172.870045] lock(rename_lock);
> [ 6172.870045] lock(rename_lock);
> [ 6172.870045]
> [ 6172.870045] *** DEADLOCK ***
> [ 6172.870045]
> [ 6172.870045] May be due to missing lock nesting notation
> [ 6172.870045]
> [ 6172.870045] 1 lock held by trinity-c55/12752:
> [ 6172.870045] #0: (rename_lock){+.+...}, at: d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045]
> [ 6172.870045] stack backtrace:
> [ 6172.870045] CPU: 1 PID: 12752 Comm: trinity-c55 Not tainted 3.18.0-rc1-next-20141023-sasha-00036-g4dcabd5 #1415
> [ 6172.870045] ffff88070945b000 0000000000000000 ffffffffb6312fd0 ffff8806d69ff728
> [ 6172.870045] ffffffffa8ff75ca 0000000000000011 ffffffffb6312fd0 ffff8806d69ff828
> [ 6172.870045] ffffffff9f3a012b ffff880107fd76c0 ffff880107fd76c0 0000000000000001
> [ 6172.870045] Call Trace:
> [ 6172.870045] dump_stack (lib/dump_stack.c:52)
> [ 6172.870045] validate_chain.isra.10 (kernel/locking/lockdep.c:2134)
> [ 6172.870045] ? kvm_clock_read (./arch/x86/include/asm/preempt.h:90 arch/x86/kernel/kvmclock.c:86)
> [ 6172.870045] ? sched_clock_cpu (kernel/sched/clock.c:311)
> [ 6172.870045] __lock_acquire (kernel/locking/lockdep.c:3184)
> [ 6172.870045] lock_acquire (./arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3604)
> [ 6172.870045] ? d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045] ? put_lock_stats.isra.7 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
> [ 6172.870045] _raw_spin_lock (include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:151)
> [ 6172.870045] ? d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045] d_walk (include/linux/spinlock.h:309 fs/dcache.c:1035)
> [ 6172.870045] ? d_walk (fs/dcache.c:1087)
> [ 6172.870045] ? d_drop (fs/dcache.c:1336)
> [ 6172.870045] ? select_collect (fs/dcache.c:1323)
> [ 6172.870045] d_invalidate (fs/dcache.c:1381)
> [ 6172.870045] lookup_fast (fs/namei.c:1440)
> [ 6172.870045] ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:183)
> [ 6172.870045] ? lockref_put_or_lock (lib/lockref.c:135)
> [ 6172.870045] ? dput (fs/dcache.c:626)
> [ 6172.870045] walk_component (fs/namei.c:1545)
> [ 6172.870045] ? security_inode_permission (security/security.c:573)
> [ 6172.870045] ? __inode_permission (fs/namei.c:418)
> [ 6172.870045] link_path_walk (fs/namei.c:1805)
> [ 6172.870045] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
> [ 6172.870045] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2559 kernel/locking/lockdep.c:2601)
> [ 6172.870045] ? getname_flags (fs/namei.c:145)
> [ 6172.870045] path_lookupat (fs/namei.c:1956)
> [ 6172.870045] ? kmem_cache_alloc (include/linux/rcupdate.h:479 include/trace/events/kmem.h:53 mm/slub.c:2463)
> [ 6172.870045] ? getname_flags (fs/namei.c:145)
> [ 6172.870045] filename_lookup (fs/namei.c:2000)
> [ 6172.870045] user_path_at_empty (fs/namei.c:2151)
> [ 6172.870045] ? preempt_count_sub (kernel/sched/core.c:2662)
> [ 6172.870045] user_path_at (fs/namei.c:2162)
> [ 6172.870045] vfs_fstatat (fs/stat.c:106)
> [ 6172.870045] SYSC_newlstat (fs/stat.c:284)
> [ 6172.870045] ? syscall_trace_enter_phase2 (arch/x86/kernel/ptrace.c:1598)
> [ 6172.870045] ? tracesys_phase2 (arch/x86/kernel/entry_64.S:518)
> [ 6172.870045] SyS_newlstat (fs/stat.c:277)
> [ 6172.870045] tracesys_phase2 (arch/x86/kernel/entry_64.S:529)
>
> The machine proceeded to actually lock up, so this isn't a false positive.
>
>
> Thanks,
> Sasha
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