diff options
| author | Palmer Dabbelt <palmer@sifive.com> | 2017-12-05 17:48:11 -0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@dabbelt.com> | 2017-12-11 07:51:07 -0800 |
| commit | 3cfa5008081db845c6c53d531ec34e9c84a9fd99 (patch) | |
| tree | 805a705c5ab4544fe0bb8402a21433805a502f7e /arch/riscv | |
| parent | 86ad5c97ce5ccdda1459d35370fd5e105721bb8d (diff) | |
RISC-V: Resurrect smp_mb__after_spinlock()
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: 3343eb6806f3 ("RISC-V: Remove smb_mb__{before,after}_spinlock()")
CC: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Diffstat (limited to 'arch/riscv')
| -rw-r--r-- | arch/riscv/include/asm/barrier.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/barrier.h b/arch/riscv/include/asm/barrier.h index 773c4e039cd7..c0319cbf1eec 100644 --- a/arch/riscv/include/asm/barrier.h +++ b/arch/riscv/include/asm/barrier.h @@ -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__ */ |