On Mon, Oct 09, 2017 at 08:46:56AM -0700, Paul E. McKenney wrote: > On Mon, Oct 09, 2017 at 04:47:08PM +0200, Christian Borntraeger wrote: > > PID: 84 TASK: 3305a00 CPU: 2 COMMAND: "sh" > > LOWCORE INFO: > > -psw : 0x0404c00180000000 0x00000000001163a6 > > -function : smp_yield_cpu at 1163a6 > > -prefix : 0x7d780000 > > -cpu timer: 0x7fffffecf69f4974 > > -clock cmp: 0x42e71c731cb22c00 > > > > #0 [033476e0] arch_spin_lock_wait at 850298 > > #1 [03347738] lock_timer_base at 1e4d22 > > #2 [033477a0] mod_timer at 1e5f2c > > #3 [03347810] __sclp_vt220_write at 6ba912 > > #4 [033478a0] sclp_vt220_con_write at 6ba9ac > > #5 [033478f8] console_unlock at 1c87c8 > > #6 [03347978] vprintk_emit at 1c8bbe > > #7 [03347a08] vprintk_default at 1c8e1c > > #8 [03347a68] printk at 1c9d1e > > #9 [03347af8] timers_dead_cpu at 1e66f6 > > #10 [03347b68] cpuhp_invoke_callback at 169b50 > > #11 [03347c00] _cpu_down at 851522 > > #12 [03347c58] do_cpu_down at 16b9fa > > #13 [03347c88] device_offline at 5a7826 > > #14 [03347cc0] online_store at 5a796e > > #15 [03347cf8] kernfs_fop_write at 3ed8d2 > > #16 [03347d48] __vfs_write at 34ddb6 > > #17 [03347e00] vfs_write at 34e10c > > #18 [03347e60] sys_write at 34e44e > > #19 [03347ea8] system_call at 85abf4 > > > > > > Reverting the patch fixes the issue, but I do not yet understand why. > > Welcome to my world! ;-) > > Hmmm... I have to ask... Have you tried this with lockdep? The spinning > on CPUs is suspicious, though not something that I have seen. This seems to simply deadlock because the cpu tries to grab a timer_base lock twice: first in timers_dead_cpu() and then via the new pr_info() within migrate_timer_list(). That one get's into our sclp device driver which tries to enqueue a timer and needs to grap a timer_base lock as well. Which appearently seems to be the same lock that was taken within timers_dead_cpu(). -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
