Messages in this thread | | | Date | Wed, 6 Jan 2016 11:21:46 +0100 | From | Jan Kara <> | Subject | Re: [PATCH 1/7] printk: Hand over printing to console if printing too long |
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On Wed 06-01-16 17:36:53, Sergey Senozhatsky wrote: > On (01/06/16 12:38), Sergey Senozhatsky wrote: > > On (01/05/16 15:48), Jan Kara wrote: > > > > [..] > > > > > cond_resched() does its job there, of course. well, a user process still can > > > > > do a lot of call_console_drivers() calls. may be we can check who is calling > > > > > console_unlock() and if we have "!printk_sync && !oops_in_progress" (or just printk_sync > > > > > test) AND a user process then return from console_unlock() doing irq_work_queue() > > > > > and set PRINTK_PENDING_OUTPUT pending bit, the way vprintk_emit() does it. > > > > > > > > attached two patches, I ended up having on top of yours. just in case. > > > > > > > > printk: factor out can_printk_async() > > > > > > > > console_unlock() can be called directly or indirectly by a user > > > > space process, so it can end up doing call_console_drivers() loop, > > > > which will hold it from returning back to user-space from a syscall > > > > for unpredictable amount of time. > > > > > > > > Factor out can_printk_async() function, which queues an irq work and > > > > sets a PRINTK_PENDING_OUTPUT pending bit (if we can do async printk). > > > > vprintk_emit() already does it, add can_printk_async() call to > > > > console_unlock() for !PF_KTHREAD processes. > > > > > > I'd be cautious about changing this userspace visible behavior. Someone may > > > be relying on it... I agree that sometimes we can block userspace process > > > in kernel for a long time (e.g. in my testing I often see syslog process > > > doing the printing) but so far I didn't see / was notified about some real > > > problem with this. So unless I see some real user issues with user > > > processes doing printing for too long I would not touch this. > > > > and w/o a lot of effort (no heavy printk message traffic) > > or like this on another setup ([k|u]_ts updated to u64) > > # cat /proc/1/time_in_console_unlock > kern:[12.755920] user:[38.367332]
So maybe that is worth addressing if it bothers you but please as a separate patch set. This seems fairly independent and I think even current version of the patches will be controversial enough...
Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR
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