Hello Steven, On (11/08/17 09:29), Steven Rostedt wrote: > On Wed, 8 Nov 2017 14:19:55 +0900 > Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> wrote: > > > the change goes further. I did express some of my concerns during the KS, > > I'll just bring them to the list. > > > > > > we now always shift printing from a save - scheduleable - context to > > a potentially unsafe one - atomic. by example: > > And vice versa. We are now likely to go from a unscheduleable context > to a schedule one, where before, that didn't exist. the existence of "and vice versa" is kinda alarming, isn't it? it's sort of "yes, we can break some things, but we also can improve some things." > And my approach, makes it more likely that the task doing the printk > prints its own message, and less likely to print someone else's. > > > > > CPU0 CPU1~CPU10 CPU11 > > > > console_lock() > > > > printk(); > > > > console_unlock() IRQ > > set console_owner printk() > > sees console_owner > > set console_waiter > > sees console_waiter > > break > > console_unlock() > > ^^^^ lockup [?] > > How? oh, yes, the missing part - assume CPU1~CPU10 did 5000 printk() calls, while console_sem was locked on CPU0. then we console_unlock() from CPU0 and shortly after IRQ->printk() from CPU11 forcibly takes over, so now we are in console_unlock() from atomic, printing some 5000 messages. -ss -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
