2013/11/25 Axel Lin <axel....@ingics.com>:
> I'm testing on a nommu platform (arm7tdmi SoC).
> Using current Linus' tree + out-of-tree patches for this SoC.
> I got below hang while executing ls (busybox) after boot.
>
> / # ls
> [ 51.036191] ------------[ cut here ]------------
> [ 51.042242] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:3312
> lock_set_class+0x5c8/0x660()
> [ 51.051426] DEBUG_LOCKS_WARN_ON(!depth)
> [ 51.055842] CPU: 0 PID: 1 Comm: Not tainted
> 3.13.0-rc1-00100-g4b061f7-dirty #1917
> [ 51.065415] [<0000c430>] (unwind_backtrace+0x0/0xe0) from [<0000ae58>]
> (show_stack+0x10/0x14)
> [ 51.075781] [<0000ae58>] (show_stack+0x10/0x14) from [<0000f7b0>]
> (warn_slowpath_common+0x58/0x78)
> [ 51.086549] [<0000f7b0>] (warn_slowpath_common+0x58/0x78) from
> [<0000f814>] (warn_slowpath_fmt+0x2c/0x3c)
> [ 51.098162] [<0000f814>] (warn_slowpath_fmt+0x2c/0x3c) from [<00036d9c>]
> (lock_set_class+0x5c8/0x660)
> [ 50.934805] [<00036d9c>] (lock_set_class+0x5c8/0x660) from [<000367d4>]
> (lock_set_class+0x0/0x660)
> [ 50.945255] [<000367d4>] (lock_set_class+0x0/0x660) from [<00000000>] (
> (null))
> [ 50.953242] ---[ end trace 7d1e4eb800000001 ]---
>
Now test on top of linux-3.13-rc3.
I found I can hit this lockdep warning only when CONFIG_PREEMPT_NONE=y
1) With CONFIG_PREEMPT_NONE=y
executing ls (busybox) hang with above lockdep warning.
2) With CONFIG_PREEMPT_VOLUNTARY=y:
have "[sched_delayed] sched: RT throttling activated" in boot message.
executing ls (busybox) hang silently.
3) With CONFIG_PREEMPT=y:
executing ls (busybox) successfully and it's ok to execute other binary.
all the test with below configs:
CONFIG_PREEMPT_COUNT=y
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
CONFIG_LOCKDEP=y
CONFIG_DEBUG_ATOMIC_SLEEP=y
CONFIG_TRACE_IRQFLAGS=y
CONFIG_STACKTRACE=y
CONFIG_DEBUG_BUGVERBOSE=y
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