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kernel/arm: fix missing interrupt lock around _is_next_thread_current()

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This reverts commit

	"kernel/arm: add comment about _is_next_thread_current"

and fixes the interrupt locking issue.

The comment would have been right if only reads were done the ready
queue, but that is not the case. It turns out that the comment was written
ignoring the fact that _is_next_thread_current() updates the next thread
cache when fetching the next thread.

Change-Id: I21c9230f85f4f87a6bbf14fd4a9eb7e19b59f8c5
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>
This commit is contained in:
Benjamin Walsh 2016-11-15 15:26:23 -05:00 • committed by Anas Nashif
commit 13f6a0c676
1 changed files with 3 additions and 21 deletions
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24
arch/arm/core/exc_exit.S
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@ -104,28 +104,10 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
push {lr}
/*
* _is_next_thread_current() calls _get_next_ready_thread(), which is
* supposed to be called only with interrupts locked: interrupts are _not_
* locked at this point. However, that is not a problem in this case:
*
* - Threads can only be added to the ready queue in an ISR, not removed.
* Thus, priorities with runnable thread can only be added as well.
*
* - The PendSV handler is the context that will decide which thread to
* run, not the current context.
*
* - The current decision to pend PendSV or not is started with the ready
* queue state that the currently exiting ISR updated: if that state
* changes, it can only be to add a thread as runnable, not remove one.
*
* - The only discrepancy that can happen is if another ISR preempts the
* current one and makes another thread than the current the next thread
* to run, if the current ISR did not do already that. In that case, even
* if the decision is interrupted, the current code running in the higher
* priority ISR _will_ take the correct decision to pend PendSV.
*/
/* _is_next_thread_current must be called with interrupts locked */
cpsid i
blx _is_next_thread_current
cpsie i
#if defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
pop {r1}
mov lr, r1