This is a note to let you know that I've just added the patch titled
rtc: cmos: avoid taking rtc_lock for extended period of time
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rtc-cmos-avoid-taking-rtc_lock-for-extended-period-o.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 17d773cfab06eb96c70c0b688b8141e59d4e3d61
Author: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Date: Fri Oct 25 13:14:57 2024 -0700
rtc: cmos: avoid taking rtc_lock for extended period of time
[ Upstream commit 0a6efab33eab4e973db26d9f90c3e97a7a82e399 ]
On my device reading entirety of /sys/devices/pnp0/00:03/cmos_nvram0/nvmem
takes about 9 msec during which time interrupts are off on the CPU that
does the read and the thread that performs the read can not be migrated
or preempted by another higher priority thread (RT or not).
Allow readers and writers be preempted by taking and releasing rtc_lock
spinlock for each individual byte read or written rather than once per
read/write request.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Reviewed-by: Mateusz Jończyk <mat.jonczyk@xxxxx>
Link: https://lore.kernel.org/r/Zxv8QWR21AV4ztC5@xxxxxxxxxx
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 542568cd72b32..5f43773900d18 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -645,18 +645,17 @@ static int cmos_nvram_read(void *priv, unsigned int off, void *val,
unsigned char *buf = val;
off += NVRAM_OFFSET;
- spin_lock_irq(&rtc_lock);
- for (; count; count--, off++) {
+ for (; count; count--, off++, buf++) {
+ guard(spinlock_irq)(&rtc_lock);
if (off < 128)
- *buf++ = CMOS_READ(off);
+ *buf = CMOS_READ(off);
else if (can_bank2)
- *buf++ = cmos_read_bank2(off);
+ *buf = cmos_read_bank2(off);
else
- break;
+ return -EIO;
}
- spin_unlock_irq(&rtc_lock);
- return count ? -EIO : 0;
+ return 0;
}
static int cmos_nvram_write(void *priv, unsigned int off, void *val,
@@ -671,23 +670,23 @@ static int cmos_nvram_write(void *priv, unsigned int off, void *val,
* NVRAM to update, updating checksums is also part of its job.
*/
off += NVRAM_OFFSET;
- spin_lock_irq(&rtc_lock);
- for (; count; count--, off++) {
+ for (; count; count--, off++, buf++) {
/* don't trash RTC registers */
if (off == cmos->day_alrm
|| off == cmos->mon_alrm
|| off == cmos->century)
- buf++;
- else if (off < 128)
- CMOS_WRITE(*buf++, off);
+ continue;
+
+ guard(spinlock_irq)(&rtc_lock);
+ if (off < 128)
+ CMOS_WRITE(*buf, off);
else if (can_bank2)
- cmos_write_bank2(*buf++, off);
+ cmos_write_bank2(*buf, off);
else
- break;
+ return -EIO;
}
- spin_unlock_irq(&rtc_lock);
- return count ? -EIO : 0;
+ return 0;
}
/*----------------------------------------------------------------*/
