On Mon, Oct 30, 2017 at 07:09:21PM +0900, Byungchul Park wrote:
> On Mon, Oct 30, 2017 at 09:22:03AM +0100, Michal Hocko wrote:
> > [Cc Byungchul. The original full report is
> > http://lkml.kernel.org/r/[email protected]]
> >
> > Could you have a look please? This smells like a false positive to me.
>
> +cc [email protected]
>
> Hello,
>
> IMHO, the false positive was caused by the lockdep_map of 'cpuhp_state'
> which couldn't distinguish between cpu-up and cpu-down.
>
> And it was solved with the following commit by Peter and Thomas:
>
> 5f4b55e10645b7371322c800a5ec745cab487a6c
> smp/hotplug: Differentiate the AP-work lockdep class between up and down
>
> Therefore, we can avoid the false positive on later than the commit.
>
> Peter and Thomas, could you confirm it?
I can indeed confirm it's running old code; cpuhp_state is no more.
However, that splat translates like:
__cpuhp_setup_state()
#0 cpus_read_lock()
__cpuhp_setup_state_cpuslocked()
#1 mutex_lock(&cpuhp_state_mutex)
__cpuhp_state_add_instance()
#2 mutex_lock(&cpuhp_state_mutex)
cpuhp_issue_call()
cpuhp_invoke_ap_callback()
#3 wait_for_completion()
msr_device_create()
...
#4 filename_create()
#3 complete()
do_splice()
#4 file_start_write()
do_splice_from()
iter_file_splice_write()
#5 pipe_lock()
vfs_iter_write()
...
#6 inode_lock()
sys_fcntl()
do_fcntl()
shmem_fcntl()
#5 inode_lock()
shmem_wait_for_pins()
if (!scan)
lru_add_drain_all()
#0 cpus_read_lock()
Which is an actual real deadlock, there is no mixing of up and down.
