Messages in this thread Patch in this message | | | Date | Fri, 04 Apr 2014 15:46:39 +0800 | From | Jet Chen <> | Subject | Re: WARNING: CPU: 0 PID: 1935 at kernel/timer.c:1621 migrate_timer_list() |
| |
Hi Viresh,
I changed your print message as you suggested.
diff --git a/kernel/timer.c b/kernel/timer.c index 6c3a371..193101d 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1617,8 +1617,8 @@ static void migrate_timer_list(struct tvec_base *new_base, struct list_head *hea
/* Check if CPU still has pinned timers */ if (unlikely(WARN(is_pinned, - "%s: can't migrate pinned timer: %p, deactivating it\n", - __func__, timer))) + "%s: can't migrate pinned timer: %p, timer->function: %p,deactivating it\n", + __func__, timer, timer->function))) continue;
Then I reproduced the issue, and got the dmesg output,
[ 37.918406] migrate_timer_list: can't migrate pinned timer: ffffffff81f06a60, timer->function: ffffffff810d7010,deactivating it We reproduced this issue for several times in our LKP system. The address of timer ffffffff81f06a60 is very constant. So is timer->function, I believe. Hope this information will help you. Please feel free to tell me what else I can do to help you.
Thanks, Jet
On 04/04/2014 12:56 PM, Viresh Kumar wrote: > Thanks Fengguang, > > On 4 April 2014 08:49, Fengguang Wu <fengguang.wu@intel.com> wrote: >> Greetings, >> >> I got the below dmesg and the first bad commit is >> >> git://git.linaro.org/people/vireshk/linux timer-cleanup-for-tglx >> >> commit 6378cb51af5f4743db0dcb3cbcf862eac5908754 >> Author: Viresh Kumar <viresh.kumar@linaro.org> >> AuthorDate: Thu Mar 20 14:29:02 2014 +0530 >> Commit: Viresh Kumar <viresh.kumar@linaro.org> >> CommitDate: Wed Apr 2 14:54:57 2014 +0530 >> >> timer: don't migrate pinned timers >> >> migrate_timer() is called when a CPU goes down and its timers are required to be >> migrated to some other CPU. Its the responsibility of the users of the timer to >> remove it before control reaches to migrate_timers(). >> >> As these were the pinned timers, the best we can do is: don't migrate these and >> report to the user as well. >> >> That's all this patch does. >> >> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> >> >> =================================================== >> PARENT COMMIT NOT CLEAN. LOOK OUT FOR WRONG BISECT! >> =================================================== >> Attached one more dmesg for the NULL pointer bug in parent commit. >> >> +--------------------------------------------------------+------------+------------+------------+ >> | | 5a8530b7c3 | 6378cb51af | 7caf71f403 | >> +--------------------------------------------------------+------------+------------+------------+ >> | boot_successes | 103 | 14 | 10 | >> | boot_failures | 17 | 18 | 13 | >> | BUG:unable_to_handle_kernel_NULL_pointer_dereference | 16 | | | >> | Oops:SMP | 16 | | | >> | Kernel_panic-not_syncing:Fatal_exception | 16 | | | >> | backtrace:vfs_read | 16 | | | >> | backtrace:SyS_read | 16 | | | >> | BUG:kernel_test_crashed | 1 | | | >> | WARNING:CPU:PID:at_kernel/timer.c:migrate_timer_list() | 0 | 17 | 12 | >> | backtrace:vfs_write | 0 | 17 | 12 | >> | backtrace:SyS_write | 0 | 17 | 12 | >> | BUG:kernel_early_hang_without_any_printk_output | 0 | 1 | 1 | >> +--------------------------------------------------------+------------+------------+------------+ >> >> [ 74.242293] Unregister pv shared memory for cpu 1 >> [ 74.273280] smpboot: CPU 1 is now offline >> [ 74.274685] ------------[ cut here ]------------ >> [ 74.275524] WARNING: CPU: 0 PID: 1935 at kernel/timer.c:1621 migrate_timer_list+0xd6/0xf0() >> [ 74.275524] migrate_timer_list: can't migrate pinned timer: ffffffff81f06a60, deactivating it > > Hmm, nice. So, my patch hasn't created a bug, but just highlighted it. > I have added this piece of code while migrating timers away: > > if (unlikely(WARN(is_pinned, > "%s: can't migrate pinned timer: %p, deactivating it\n", > __func__, timer))) > > Which means, migrate all timers to other CPUs when a CPU is going down. > But obviously we can't migrate the pinned timers. And it looks like we > actually were doing that before this commit and things went unnoticed. > > But just due to this print, we are highlighting an existing issue here. > @Thomas: So, in a sense my patch is doing some good work now :) > > Now, we need to fix the code which queued this pinned timer. > @Fengguang: As I don't have the facilities to reproduce this, can you > help me debugging this? Probably just change this print message to > print the address of timer->function as well and then we can find > the name of routine with help of objdump.. > > What we need to do finally is to remove this timer before CPU is > going down. I can fix the driver in question once we know which > driver it is. > > -- > viresh >
| |