kernel: Reset the switch_handler only in the arch code
Avoid setting the switch_handler in the z_get_next_switch_handle() code when the context is not fully saved yet to avoid a race against other cores waiting on wait_for_switch(). See issue #40795 and discussion in #41840 Signed-off-by: Carlo Caione <ccaione@baylibre.com>
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2 changed files with 39 additions and 1 deletions
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@ -119,9 +119,28 @@ spurious_continue:
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* x0: 1st thread in the ready queue
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* x1: _current thread
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*/
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#ifdef CONFIG_SMP
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/*
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* 2 possibilities here:
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* - x0 != NULL (implies x0 != x1): we need to context switch and set
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* the switch_handle in the context switch code
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* - x0 == NULL: no context switch
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*/
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cmp x0, #0x0
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bne switch
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/*
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* No context switch. Restore x0 from x1 (they are the same thread).
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* See also comments to z_arch_get_next_switch_handle()
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*/
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mov x0, x1
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b exit
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switch:
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#else
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cmp x0, x1
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beq exit
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#endif
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/* Switch thread */
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bl z_arm64_context_switch
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@ -124,9 +124,28 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
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void *z_arch_get_next_switch_handle(struct k_thread **old_thread)
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{
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/*
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* When returning from this function we will have the current thread
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* onto the stack to be popped in x1 and the next thread in x0 returned
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* from z_get_next_switch_handle() (see isr_wrapper.S)
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*/
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*old_thread = _current;
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#ifdef CONFIG_SMP
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/*
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* XXX: see thread in #41840 and #40795
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*
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* The scheduler API requires a complete switch handle here, but arm64
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* optimizes things such that the callee-save registers are still
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* unsaved here (they get written out in z_arm64_context_switch()
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* below). So pass a NULL instead, which the scheduler will store into
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* the thread switch_handle field. The resulting thread won't be
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* switched into until we write that ourselves.
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*/
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return z_get_next_switch_handle(NULL);
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#else
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return z_get_next_switch_handle(*old_thread);
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#endif
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}
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#ifdef CONFIG_USERSPACE
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