Unverified Commit 38b7c2a3 authored by Palmer Dabbelt's avatar Palmer Dabbelt
Browse files

RISC-V: Upgrade smp_mb__after_spinlock() to iorw,iorw 



While digging through the recent mmiowb preemption issue it came up that
we aren't actually preventing IO from crossing a scheduling boundary.
While it's a bit ugly to overload smp_mb__after_spinlock() with this
behavior, it's what PowerPC is doing so there's some precedent.

Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent 0cac21b0

arch/riscv/include/asm/barrier.h

+9 −1
Original line number Diff line number Diff line
@@ -58,8 +58,16 @@ do { \ 
 * The AQ/RL pair provides a RCpc critical section, but there's not really any

 * way we can take advantage of that here because the ordering is only enforced

 * on that one lock.  Thus, we're just doing a full fence.

 *

 * Since we allow writeX to be called from preemptive regions we need at least

 * an "o" in the predecessor set to ensure device writes are visible before the

 * task is marked as available for scheduling on a new hart.  While I don't see

 * any concrete reason we need a full IO fence, it seems safer to just upgrade

 * this in order to avoid any IO crossing a scheduling boundary.  In both

 * instances the scheduler pairs this with an mb(), so nothing is necessary on

 * the new hart.

 */

#define smp_mb__after_spinlock()	RISCV_FENCE(rw,rw)

#define smp_mb__after_spinlock()	RISCV_FENCE(iorw,iorw)



#include <asm-generic/barrier.h>

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