On Mon, Mar 22, 2021 at 05:59:17PM +0100, Sebastian Andrzej Siewior wrote: > On 2021-03-22 12:42:00 [-0400], Alan Stern wrote: > > What happens on RT systems? Are they smart enough to avoid the whole > > problem by enabling interrupts during _all_ callbacks? > > tl;dr: Yes. > > The referenced commit (id 81e2073c175b) disables interrupts only on !RT > configs so for RT everything remains unchanged (the backports are > already adjusted for the old stable trees to use the proper CONFIG_* for > enabled RT). > > All hrtimer callbacks run as HRTIMER_MODE_SOFT by default. The > HRTIMER_MODE_HARD ones (which expire in HARDIRQ context) were audited / > explicitly enabled. > The same goes irq_work. > The printk code is different compared to mainline. A printk() on RT in > HARDIRQ context is printed once the HARDIRQ context is left. So the > serial/console/… driver never gets a chance to acquire its lock in > hardirq context. > > An interrupt handler which is not forced-threaded must be marked as such > and must not use any spinlock_t based locking. lockdep/might_sleep > complain here already. Okay, in that case: Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
