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USB: serial: relax unthrottle memory barrier

PATCH In review Johan Hovold 3 participants 4 messages Jan 30, 2020 – Feb 10, 2020

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USB USB serial
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Johan Hovold

author maintainer
#0 lore raw

PATCH 1/1 USB: serial: relax unthrottle memory barrier

Commit a8d78d9f3856 ("USB: serial: clean up throttle handling") converted the throttle handling to use atomic bitops. This means that we can relax the smp_mb() in unthrottle() to smp_mb__after_atomic(), which for example is a no-op on architectures like x86 that provide fully ordered atomics.

Signed-off-by Johan Hovold <[email protected]>
---
 drivers/usb/serial/generic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
drivers/usb/serial/generic.c +2 -2
index 1be8bea372a2..546a1c2ce2f2 100644
@@ -417,7 +417,7 @@ void usb_serial_generic_read_bulk_callback(struct urb *urb)
 	/*
 	 * Make sure URB is marked as free before checking the throttled flag
 	 * to avoid racing with unthrottle() on another CPU. Matches the
-	 * smp_mb() in unthrottle().
+	 * smp_mb__after_atomic() in unthrottle().
 	 */
 	smp_mb__after_atomic();
 

@@ -489,7 +489,7 @@ void usb_serial_generic_unthrottle(struct tty_struct *tty)
 	 * Matches the smp_mb__after_atomic() in
 	 * usb_serial_generic_read_bulk_callback().
 	 */
-	smp_mb();
+	smp_mb__after_atomic();
 
 	usb_serial_generic_submit_read_urbs(port, GFP_KERNEL);
 }
Signature · 1 line
2.24.1
Reviewed-by Greg Kroah-Hartman on v1 1/1
#1 lore raw
Quoted 7 lines · Johan Hovold

Commit a8d78d9f3856 ("USB: serial: clean up throttle handling") converted the throttle handling to use atomic bitops. This means that we can relax the smp_mb() in unthrottle() to smp_mb__after_atomic(), which for example is a no-op on architectures like x86 that provide fully ordered atomics.

Signed-off-by Johan Hovold <[email protected]>
Reviewed-by Greg Kroah-Hartman <[email protected]>
Reviewed-by on v1 1/1
#2 lore raw
In reply to Johan Hovold
Quoted 7 lines · Johan Hovold

Commit a8d78d9f3856 ("USB: serial: clean up throttle handling") converted the throttle handling to use atomic bitops. This means that we can relax the smp_mb() in unthrottle() to smp_mb__after_atomic(), which for example is a no-op on architectures like x86 that provide fully ordered atomics.

Signed-off-by Johan Hovold <[email protected]>
Reviewed-by Davidlohr Bueso <[email protected]>
author maintainer
#3 lore raw
Quoted 11 lines · Davidlohr Bueso
Quoted 7 lines · Johan Hovold

Commit a8d78d9f3856 ("USB: serial: clean up throttle handling") converted the throttle handling to use atomic bitops. This means that we can relax the smp_mb() in unthrottle() to smp_mb__after_atomic(), which for example is a no-op on architectures like x86 that provide fully ordered atomics.

Signed-off-by Johan Hovold <[email protected]>
Reviewed-by Davidlohr Bueso <[email protected]>

Thanks for the review. Now applied.

Johan