[PATCH AUTOSEL 6.11 2/7] rtc: cmos: avoid taking rtc_lock for extended period of time

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>

[ 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>
---
 drivers/rtc/rtc-cmos.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 35dca2accbb8d..5849d2970bba4 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;
 }
 
 /*----------------------------------------------------------------*/
-- 
2.43.0





[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux