RISC-V: Resurrect smp_mb__after_spinlock() (3cfa5008) · Commits · 戴 / test

I removed this last week because of an incorrect comment: smp_mb__after_spinlock() is actually still used, and is necessary on RISC-V. It's been resurrected, with a comment that describes what it actually does this time. Thanks to Andrea for finding the bug! Fixes: ("RISC-V: Remove smb_mb__{before,after}_spinlock()") CC: Andrea Parri <parri.andrea@gmail.com> Signed-off-by:

Palmer Dabbelt <palmer@sifive.com>

arch/riscv/include/asm/barrier.h

+19 −0

Original line number	Diff line number	Diff line
		@@ -38,6 +38,25 @@
		#define smp_rmb() RISCV_FENCE(r,r)
		#define smp_wmb() RISCV_FENCE(w,w)

		/*
		* This is a very specific barrier: it's currently only used in two places in
		* the kernel, both in the scheduler. See include/linux/spinlock.h for the two
		* orderings it guarantees, but the "critical section is RCsc" guarantee
		* mandates a barrier on RISC-V. The sequence looks like:
		*
		* lr.aq lock
		* sc lock <= LOCKED
		* smp_mb__after_spinlock()
		* // critical section
		* lr lock
		* sc.rl lock <= UNLOCKED
		*
		* 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.
		*/
		#define smp_mb__after_spinlock() RISCV_FENCE(rw,rw)

		#include <asm-generic/barrier.h>

		#endif /* __ASSEMBLY__ */

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