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

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[ Upstream commit 38b7c2a3ffb1fce8358ddc6006cfe5c038ff9963 ]

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: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Palmer Dabbelt 2020-07-16 11:57:26 -07:00 committed by Greg Kroah-Hartman
parent 5345ede4ac
commit 35728cac17
1 changed files with 9 additions and 1 deletions
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10
arch/riscv/include/asm/barrier.h
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@ -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>