Hi Yu, On 8/18/25 9:56 AM, Yu Kuai wrote: > Hi, > > 在 2025/08/17 19:31, Yunseong Kim 写道: >> The function ppl_io_unit_finished() uses a local_irq_save()/spin_lock() >> sequence. On a PREEMPT_RT enabled kernel, spin_lock() can sleep. Calling it >> with interrupts disabled creates an atomic context where sleeping is >> forbidden. >> > What? I believe spin_lock can never sleep. I think you might have been a bit surprised by me sending a patch out of the blue. It would be helpful to refer to the references below: On PREEMPT_RT kernels, these lock types are converted to sleeping locks: local_lock spinlock_t rwlock_t Link: https://docs.kernel.org/locking/locktypes.html#sleeping-locks >> Ensuring that the interrupt state is managed atomically with the lock >> itself. The change is applied to both the 'log->io_list_lock' and >> 'ppl_conf->no_mem_stripes_lock' critical sections within the function. >> >> Signed-off-by: Yunseong Kim <ysk@xxxxxxxxxxx> >> --- >> drivers/md/raid5-ppl.c | 12 ++++-------- >> 1 file changed, 4 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/md/raid5-ppl.c b/drivers/md/raid5-ppl.c >> index 56b234683ee6..650bd59ead72 100644 >> --- a/drivers/md/raid5-ppl.c >> +++ b/drivers/md/raid5-ppl.c >> @@ -553,15 +553,13 @@ static void ppl_io_unit_finished(struct ppl_io_unit *io) >> pr_debug("%s: seq: %llu\n", __func__, io->seq); >> - local_irq_save(flags); >> - >> - spin_lock(&log->io_list_lock); >> + spin_lock_irqsave(&log->io_list_lock, flags); The changes in spinlock_t and rwlock_t semantics on PREEMPT_RT kernels have a few implications. For example, on a non-PREEMPT_RT kernel the following code sequence works as expected: local_irq_disable(); spin_lock(&lock); and is fully equivalent to: spin_lock_irq(&lock); Same applies to rwlock_t and the _irqsave() suffix variants. Link: https://docs.kernel.org/locking/locktypes.html#spinlock-t-and-rwlock-t >> list_del(&io->log_sibling); >> - spin_unlock(&log->io_list_lock); >> + spin_unlock_irqrestore(&log->io_list_lock, flags); >> mempool_free(io, &ppl_conf->io_pool); >> - spin_lock(&ppl_conf->no_mem_stripes_lock); >> + spin_lock_irqsave(&ppl_conf->no_mem_stripes_lock, flags); > > Please notice, local_irq_save + spin_lock is the same as > spin_lock_irqsave, I don't think your changes have any functonal > chagnes. This issue has also been a problem in other subsystems, such as USB: [BUG] usb: gadget: dummy_hcd: Sleeping function called from invalid context in dummy_dequeue on PREEMPT_RT Link: https://lore.kernel.org/lkml/20250816065933.EPwBJ0Sd@xxxxxxxxxxxxx/t/#u I am currently contributing to the kernel to address the areas that need to adapt to this paradigm shift so that the PREEMPT_RT Linux kernel can be well supported. I have CC’d other RT people so they can also review this part. > Thanks, > Kuai Thank you! Yunseong
