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Clear the exclusive monitor when returning from an exception
The patch adds a CLREX or dummy STREX to the exception return path. This is needed because several atomic/locking operations use a pair of LDREX/STREXEQ and the EQ condition may not always be satisfied. This would leave the exclusive monitor status set and may cause problems with atomic/locking operations in the interrupted code. With this patch, the atomic_set() operation can be a simple STR instruction (on SMP systems, the global exclusive monitor is cleared by STR anyway). Clearing the exclusive monitor during context switch is no longer needed as this is handled by the exception return path anyway. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Reported-by: Jamie Lokier <jamie@shareable.org>
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df58bee21e
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arch/arm
@ -19,31 +19,21 @@
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#ifdef __KERNEL__
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#ifdef __KERNEL__
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/*
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* On ARM, ordinary assignment (str instruction) doesn't clear the local
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* strex/ldrex monitor on some implementations. The reason we can use it for
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* atomic_set() is the clrex or dummy strex done on every exception return.
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*/
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#define atomic_read(v) ((v)->counter)
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#define atomic_read(v) ((v)->counter)
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#define atomic_set(v,i) (((v)->counter) = (i))
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#if __LINUX_ARM_ARCH__ >= 6
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#if __LINUX_ARM_ARCH__ >= 6
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/*
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/*
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* ARMv6 UP and SMP safe atomic ops. We use load exclusive and
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* ARMv6 UP and SMP safe atomic ops. We use load exclusive and
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* store exclusive to ensure that these are atomic. We may loop
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* store exclusive to ensure that these are atomic. We may loop
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* to ensure that the update happens. Writing to 'v->counter'
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* to ensure that the update happens.
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* without using the following operations WILL break the atomic
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* nature of these ops.
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*/
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*/
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static inline void atomic_set(atomic_t *v, int i)
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{
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unsigned long tmp;
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__asm__ __volatile__("@ atomic_set\n"
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"1: ldrex %0, [%1]\n"
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" strex %0, %2, [%1]\n"
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" teq %0, #0\n"
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" bne 1b"
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: "=&r" (tmp)
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: "r" (&v->counter), "r" (i)
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: "cc");
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}
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static inline void atomic_add(int i, atomic_t *v)
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static inline void atomic_add(int i, atomic_t *v)
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{
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{
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unsigned long tmp;
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unsigned long tmp;
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@ -163,8 +153,6 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
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#error SMP not supported on pre-ARMv6 CPUs
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#error SMP not supported on pre-ARMv6 CPUs
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#endif
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#endif
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#define atomic_set(v,i) (((v)->counter) = (i))
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static inline int atomic_add_return(int i, atomic_t *v)
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static inline int atomic_add_return(int i, atomic_t *v)
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{
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{
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unsigned long flags;
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unsigned long flags;
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@ -734,13 +734,6 @@ ENTRY(__switch_to)
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#ifdef CONFIG_MMU
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#ifdef CONFIG_MMU
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ldr r6, [r2, #TI_CPU_DOMAIN]
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ldr r6, [r2, #TI_CPU_DOMAIN]
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#endif
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#endif
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#if __LINUX_ARM_ARCH__ >= 6
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#ifdef CONFIG_CPU_32v6K
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clrex
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#else
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strex r5, r4, [ip] @ Clear exclusive monitor
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#endif
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#endif
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#if defined(CONFIG_HAS_TLS_REG)
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#if defined(CONFIG_HAS_TLS_REG)
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mcr p15, 0, r3, c13, c0, 3 @ set TLS register
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mcr p15, 0, r3, c13, c0, 3 @ set TLS register
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#elif !defined(CONFIG_TLS_REG_EMUL)
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#elif !defined(CONFIG_TLS_REG_EMUL)
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@ -76,13 +76,25 @@
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#ifndef CONFIG_THUMB2_KERNEL
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#ifndef CONFIG_THUMB2_KERNEL
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.macro svc_exit, rpsr
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.macro svc_exit, rpsr
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msr spsr_cxsf, \rpsr
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msr spsr_cxsf, \rpsr
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#if defined(CONFIG_CPU_32v6K)
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clrex @ clear the exclusive monitor
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ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
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ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
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#elif defined (CONFIG_CPU_V6)
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ldr r0, [sp]
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strex r1, r2, [sp] @ clear the exclusive monitor
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ldmib sp, {r1 - pc}^ @ load r1 - pc, cpsr
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#endif
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.endm
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.endm
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.macro restore_user_regs, fast = 0, offset = 0
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.macro restore_user_regs, fast = 0, offset = 0
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ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
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ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
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ldr lr, [sp, #\offset + S_PC]! @ get pc
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ldr lr, [sp, #\offset + S_PC]! @ get pc
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msr spsr_cxsf, r1 @ save in spsr_svc
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msr spsr_cxsf, r1 @ save in spsr_svc
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#if defined(CONFIG_CPU_32v6K)
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clrex @ clear the exclusive monitor
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#elif defined (CONFIG_CPU_V6)
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strex r1, r2, [sp] @ clear the exclusive monitor
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#endif
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.if \fast
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.if \fast
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ldmdb sp, {r1 - lr}^ @ get calling r1 - lr
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ldmdb sp, {r1 - lr}^ @ get calling r1 - lr
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.else
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.else
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@ -98,6 +110,7 @@
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.endm
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.endm
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#else /* CONFIG_THUMB2_KERNEL */
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#else /* CONFIG_THUMB2_KERNEL */
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.macro svc_exit, rpsr
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.macro svc_exit, rpsr
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clrex @ clear the exclusive monitor
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ldr r0, [sp, #S_SP] @ top of the stack
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ldr r0, [sp, #S_SP] @ top of the stack
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ldr r1, [sp, #S_PC] @ return address
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ldr r1, [sp, #S_PC] @ return address
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tst r0, #4 @ orig stack 8-byte aligned?
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tst r0, #4 @ orig stack 8-byte aligned?
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@ -110,6 +123,7 @@
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.endm
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.endm
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.macro restore_user_regs, fast = 0, offset = 0
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.macro restore_user_regs, fast = 0, offset = 0
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clrex @ clear the exclusive monitor
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mov r2, sp
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mov r2, sp
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load_user_sp_lr r2, r3, \offset + S_SP @ calling sp, lr
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load_user_sp_lr r2, r3, \offset + S_SP @ calling sp, lr
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ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
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ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
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