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Atomically enabling and disabling interrupts #416

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0c98e92
Atomically enabling and disabling interrupts
segfauIt Oct 8, 2025
759dd8f
Use the bang-bang idiom to map integers
segfauIt Oct 10, 2025
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30 changes: 28 additions & 2 deletions kernel/riscv.h
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,32 @@ w_sstatus(uint64 x)
asm volatile("csrw sstatus, %0" : : "r" (x));
}

static inline void
s_sstatus(uint64 x)
{
__asm__ __volatile__("csrs sstatus, %0" ::
"rK" (x) :
"memory");
}

static inline void
c_sstatus(uint64 x)
{
__asm__ __volatile__("csrc sstatus, %0" ::
"rK" (x) :
"memory");
}

static inline uint64
rc_sstatus(uint64 x)
{
__asm__ __volatile__("csrrc %0, sstatus, %1" :
"=r" (x) :
"rK" (x) :
"memory");
return x;
}

// Supervisor Interrupt Pending
static inline uint64
r_sip()
Expand Down Expand Up @@ -286,14 +312,14 @@ r_time()
static inline void
intr_on()
{
w_sstatus(r_sstatus() | SSTATUS_SIE);
s_sstatus(SSTATUS_SIE);
}

// disable device interrupts
static inline void
intr_off()
{
w_sstatus(r_sstatus() & ~SSTATUS_SIE);
c_sstatus(SSTATUS_SIE);
}

// are device interrupts enabled?
Expand Down
5 changes: 2 additions & 3 deletions kernel/spinlock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -88,11 +88,10 @@ holding(struct spinlock *lk)
void
push_off(void)
{
int old = intr_get();

// disable interrupts to prevent an involuntary context
// switch while using mycpu().
intr_off();
uint64 flags = rc_sstatus(SSTATUS_SIE);
int old = !!(flags & SSTATUS_SIE);

if(mycpu()->noff == 0)
mycpu()->intena = old;
Expand Down