On Wed, Jun 15, 2022 at 06:28:03PM +0200, Petr Mladek wrote: > There are reports that console kthreads prevented printing > messages during panic() or shutdown(), see > BugLink: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1 > BugLink: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@xxxxxxxxxxxxxx > > In both situations, printk() correctly tries to flush the consoles > directly but it fails to get the global console_lock(). Both > problems went away with these patches: > > 1st patch blocks console kthreads so that they do not start > handling new messages when the direct printing is preferred > by the system state. It is probably enough on its own. It > solves the problem when the kthreads actively did > the wrong thing. > > 2nd patch allows to wait for the console kthreads to release > the lock in any context. It should make it more reliable. > It would have been useful even for the legacy code. Thank you! For the series: Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > More possible improvements: > > + the waiting might be necessary also in the suspend code paths > > + convert con->mutex to con->spinlock to avoid blocking > the global console_lock() when sleeping with con->lock > > + at least disable preemption around console_emit_next_record() > in console kthread to avoid sleeping in the console driver > code > > + somehow change the priority of the kthread so that it gets > scheduled immediately when the scheduler works > > Petr Mladek (2): > printk: Block console kthreads when direct printing will be required > printk: Wait for the global console lock when the system is going down > > include/linux/printk.h | 5 +++++ > kernel/panic.c | 2 ++ > kernel/printk/internal.h | 2 ++ > kernel/printk/printk.c | 8 +++++++- > kernel/printk/printk_safe.c | 32 ++++++++++++++++++++++++++++++++ > kernel/reboot.c | 2 ++ > 6 files changed, 50 insertions(+), 1 deletion(-) > > -- > 2.35.3 >
