Messages in this thread | | | Subject | Re: [PATCH] debugobjects: Move printk out of db lock critical sections | From | Waiman Long <> | Date | Thu, 13 Dec 2018 17:01:01 -0500 |
| |
On 12/12/2018 06:39 PM, Andrew Morton wrote: > On Wed, 12 Dec 2018 17:28:14 -0500 Waiman Long <longman@redhat.com> wrote: > >> The db->lock is a raw spinlock and so the lock hold time is supposed >> to be short. This will not be the case when printk() is being involved >> in some of the critical sections. In order to avoid the long hold time, >> in case some messages need to be printed, the debug_object_is_on_stack() >> and debug_print_object() calls are now moved out of those critical >> sections. >> >> Holding the db->lock while calling printk() may lead to deadlock if >> printk() somehow requires the allocation/freeing of debug object that >> happens to be in the same hash bucket or a circular lock dependency >> warning from lockdep as reported in https://lkml.org/lkml/2018/12/11/143. >> >> [ 87.209665] WARNING: possible circular locking dependency detected >> [ 87.210547] 4.20.0-rc4-00057-gc96cf92 #1 Tainted: G W >> [ 87.211449] ------------------------------------------------------ >> [ 87.212405] getty/519 is trying to acquire lock: >> [ 87.213074] (____ptrval____) (&obj_hash[i].lock){-.-.}, at: debug_check_no_obj_freed+0xb4/0x302 >> [ 87.214343] >> [ 87.214343] but task is already holding lock: >> [ 87.215174] (____ptrval____) (&port_lock_key){-.-.}, at: uart_shutdown+0x3a3/0x4e2 >> [ 87.216260] >> [ 87.216260] which lock already depends on the new lock. >> >> This patch was also found to be able to fix a boot hanging problem >> when the initramfs image was switched on after a debugobjects splat >> from the EFI code. > Patch looks sensible, but I have a nit about the variable names. > >> --- a/lib/debugobjects.c >> +++ b/lib/debugobjects.c >> @@ -375,6 +375,8 @@ static void debug_object_is_on_stack(void *addr, int onstack) >> struct debug_bucket *db; >> struct debug_obj *obj; >> unsigned long flags; >> + bool debug_printobj = false; > "debug_printobject" would be better, but this code already intermingles > "obj" and "object". > >> + bool debug_chkstack = false; > Not so good. Is it debug_chkstack or debug_checkstk or ... > > This file uses "check" consistently so let's not depart from that? > Linux style is to avoid these tricky little abbreviations and to use > full words. > > ie, debug_checkstack, please. Better would be debug_check_stack. Or > simply check_stack: the "debug" doesn't add anything useful. > > Thanks for the review. I have eliminated debug_printobj in the new v2 patch.
Cheers, Longman
| |