Hi,
在 2025/8/18 19:54, Yunseong Kim 写道:
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
Yes, lessons are learned. Perhaps add a link tag in the commit message
just in case someone else will be confused?
Thanks,
Kuai
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
