Unverified Commit 9d0593da authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Palmer Dabbelt
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riscv/futex: Optimize atomic cmpxchg 



Remove redundant release/acquire barriers, optimizing the lr/sc sequence
to provide conditional RCsc synchronization, per the RVWMO.

Signed-off-by: default avatarDavidlohr Bueso <dave@stgolabs.net>
Reviewed-by: default avatarAndrea Parri <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20241113183321.491113-1-dave@stgolabs.net


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 0207244e

arch/riscv/include/asm/futex.h

+1 −1
Original line number Diff line number Diff line
@@ -85,7 +85,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, 


	__enable_user_access();

	__asm__ __volatile__ (

	"1:	lr.w.aqrl %[v],%[u]			\n"

	"1:	lr.w %[v],%[u]			        \n"

	"	bne %[v],%z[ov],3f			\n"

	"2:	sc.w.aqrl %[t],%z[nv],%[u]		\n"

	"	bnez %[t],1b				\n"