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Commit 7faa313f authored by Will Deacon's avatar Will Deacon
Browse files

arm64: preempt: Fix big-endian when checking preempt count in assembly 



Commit 39624469 ("arm64: preempt: Provide our own implementation of
asm/preempt.h") extended the preempt count field in struct thread_info
to 64 bits, so that it consists of a 32-bit count plus a 32-bit flag
indicating whether or not the current task needs rescheduling.

Whilst the asm-offsets definition of TSK_TI_PREEMPT was updated to point
to this new field, the assembly usage was left untouched meaning that a
32-bit load from TSK_TI_PREEMPT on a big-endian machine actually returns
the reschedule flag instead of the count.

Whilst we could fix this by pointing TSK_TI_PREEMPT at the count field,
we're actually better off reworking the two assembly users so that they
operate on the whole 64-bit value in favour of inspecting the thread
flags separately in order to determine whether a reschedule is needed.

Acked-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Reported-by: default avatar"kernelci.org bot" <bot@kernelci.org>
Tested-by: default avatarKevin Hilman <khilman@baylibre.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 732291c4

arch/arm64/include/asm/assembler.h

+3 −5
Original line number Diff line number Diff line
@@ -722,11 +722,9 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU 
	.macro		if_will_cond_yield_neon

#ifdef CONFIG_PREEMPT

	get_thread_info	x0

	ldr		w1, [x0, #TSK_TI_PREEMPT]

	ldr		x0, [x0, #TSK_TI_FLAGS]

	cmp		w1, #PREEMPT_DISABLE_OFFSET

	csel		x0, x0, xzr, eq

	tbnz		x0, #TIF_NEED_RESCHED, .Lyield_\@	// needs rescheduling?

	ldr		x0, [x0, #TSK_TI_PREEMPT]

	sub		x0, x0, #PREEMPT_DISABLE_OFFSET

	cbz		x0, .Lyield_\@

	/* fall through to endif_yield_neon */

	.subsection	1

.Lyield_\@ :

arch/arm64/kernel/entry.S

+2 −4
Original line number Diff line number Diff line
@@ -619,10 +619,8 @@ el1_irq: 
	irq_handler



#ifdef CONFIG_PREEMPT

	ldr	w24, [tsk, #TSK_TI_PREEMPT]	// get preempt count

	cbnz	w24, 1f				// preempt count != 0

	ldr	x0, [tsk, #TSK_TI_FLAGS]	// get flags

	tbz	x0, #TIF_NEED_RESCHED, 1f	// needs rescheduling?

	ldr	x24, [tsk, #TSK_TI_PREEMPT]	// get preempt count

	cbnz	x24, 1f				// preempt count != 0

	bl	el1_preempt

1:

#endif