Hello, no code changes, just refreshing the series so it'll be easier to pick up. added Reviwed-by-s and corrected a typo spotted by Petr.
This patch permits to change printk() to operate in completely asynchronous mode: new messages are getting upended to the kernel printk buffer, but instead of 'direct' printing the actual print job is performed by a dedicated kthread. This has the advantage that printing always happens from a schedulable context and thus we don't lockup any particular CPU or even interrupts. against next-20160513 v12: -- rename printk_kthread_can_run bool flag -- update printk_kthread_can_run comment (Petr) -- drop mutex from printk_sync_set(), sysfs writes are synchronised (Petr) v11: -- switch default to sync printk -- make `synchronous' param RW (Andrew, Jan) -- set RT priority to printk kthread (Andrew) -- correct comments (Andrew) v10: -- simplify printk_kthread_need_flush_console (Jan, Petr) v9: -- move need_flush_console assignment down in vprintk_emit (Jan) -- simplify need_flush_console assignment rules (Petr) -- clear need_flush_console in printing function (Petr) -- rename need_flush_console (Petr) v8: -- rename kthread printing function (Petr) -- clear need_flush_console in console_unlock() under logbuf (Petr) v7: -- do not set global printk_sync in panic in vrintk_emit() (Petr) -- simplify vprintk_emit(). drop some of local variables (Petr) -- move handling of LOGLEVEL_SCHED messages back to printk_deferred() so we wake_up_process()/console_trylock() in vprintk_emit() only for !in_sched messages v6: -- move wake_up_process out of logbuf lock (Jan, Byungchul) -- do not disable async printk in recursion handling code. -- rebase against next-20160321 (w/NMI patches) v5: -- make printk.synchronous RO (Petr) -- make printing_func() correct and do not use wait_queue (Petr) -- do not panic() when can't allocate printing thread (Petr) -- do not wake_up_process() only in IRQ, prefer vprintk_emit() (Jan) -- move wake_up_klogd_work_func() to a separate patch (Petr) -- move wake_up_process() under logbuf lock so printk recursion logic can help us out -- switch to sync_print mode if printk recursion occured -- drop "printk: Skip messages on oops" patch v4: -- do not directly wake_up() the printing kthread from vprintk_emit(), need to go via IRQ->wake_up() to avoid sched deadlocks (Jan) v3: -- use a dedicated kthread for printing instead of using wq (Jan, Tetsuo, Tejun) v2: - use dedicated printk workqueue with WQ_MEM_RECLAIM bit - fallback to system-wide workqueue only if allocation of printk_wq has failed - do not use system_wq as a fallback wq. both console_lock() and onsole_unlock() can spend a significant amount of time; so we need to use system_long_wq. - rework sync/!sync detection logic a) we can have deferred (in_sched) messages before we allocate printk_wq, so the only way to handle those messages is via IRQ context b) even in printk.synchronous mode, deferred messages must not be printed directly, and should go via IRQ context c) even if we allocated printk_wq and have !sync_printk mode, we must route deferred messages via IRQ context - so this adds additional bool flags to vprint_emit() and introduces a new pending bit to `printk_pending' - fix build on !PRINTK configs Jan Kara (2): printk: Make printk() completely async printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky (1): printk: make printk.synchronous param rw Documentation/kernel-parameters.txt | 12 +++ kernel/printk/printk.c | 146 +++++++++++++++++++++++++++++++++--- 2 files changed, 148 insertions(+), 10 deletions(-) -- 2.8.2.372.g63a3502