On Sat, Feb 16, 2013 at 9:05 AM, Oleg Nesterov <o...@redhat.com> wrote:
> On 02/16, Mandeep Singh Baines wrote:
>>
>> We don't need to call freezer_do_not_count() for in-kernel users
>> of CLONE_VFORK since exec will get called in bounded time.
>>
>> We don't want to call freezer_count() for in-kernel users because
>> they may be holding locks. freezer_count() calls try_to_freeze().
>> We don't want to freeze an in-kernel user because it may be
>> holding locks.
>
> I can only repeat my question ;)
>
> Who? We should not do this anyway. And __call_usermodehelper() doesn't
> afaics.
>
> OK, its caller (process_one_work) does lock_map_acquire() for
> debugging
> purposes, this can "confuse" print_held_locks_bug(). But this thread
> is
> PF_NOFREEZE ?
>
> Previously this was needed to suppress the false positive. Now that 2/5
> checks PF_NOFREEZE, why do we need this change?
>
After applying the PF_NOFREEZE check, I still get the following:
[ 1.001030] =======================================
[ 1.001039] [ BUG: lock held while trying to freeze! ]
[ 1.001048] 3.4.0 #24 Not tainted
[ 1.001053] ---------------------------------------
[ 1.001060] kworker/u:0/5 is exiting with locks still held!
[ 1.001068] 2 locks held by kworker/u:0/5:
[ 1.001073] #0: (khelper){.+.+.+}, at: [<8103896f>]
process_one_work+0x108/0
x2ee
[ 1.001095] #1: ((&sub_info->work)){+.+.+.}, at: [<8103896f>]
process_one_wo
rk+0x108/0x2ee
[ 1.001111]
[ 1.001113] stack backtrace:
[ 1.001119] Pid: 5, comm: kworker/u:0 Not tainted 3.4.0 #24
[ 1.001124] Call Trace:
[ 1.001135] [<81025bd6>] ? console_unlock+0x17a/0x18b
[ 1.001146] [<8105d68e>] debug_check_no_locks_held+0x82/0x8a
[ 1.001156] [<8102493f>] do_fork+0x20d/0x2ac
[ 1.001167] [<810366cb>] ? call_usermodehelper_setup+0x8c/0x8c
[ 1.001177] [<81008310>] kernel_thread+0x7a/0x82
[ 1.001186] [<810366cb>] ? call_usermodehelper_setup+0x8c/0x8c
[ 1.001198] [<814b45dc>] ? common_interrupt+0x3c/0x3c
[ 1.001208] [<810365e8>] __call_usermodehelper+0x3b/0x71
[ 1.001216] [<810389ce>] process_one_work+0x167/0x2ee
[ 1.001226] [<810365ad>] ? call_usermodehelper_freeinfo+0x1e/0x1e
[ 1.001235] [<81038dbc>] worker_thread+0xbd/0x18b
[ 1.001244] [<81038cff>] ? rescuer_thread+0x184/0x184
[ 1.001254] [<8103c636>] kthread+0x77/0x7c
[ 1.001264] [<8103c5bf>] ? kthread_freezable_should_stop+0x4a/0x4a
[ 1.001273] [<814b45e2>] kernel_thread_helper+0x6/0x10
Regards,
Mandeep
>> @@ -722,9 +722,11 @@ static int wait_for_vfork_done(struct task_struct
>> *child,
>> {
>> int killed;
>>
>> - freezer_do_not_count();
>> + if (!(current->flags & PF_KTHREAD))
>> + freezer_do_not_count();
>
> If I missed something and we really need this, imho this needs a comment.
>
> Oleg.
>
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