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

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Commit 3962446922 ("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: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2018-12-11 13:41:32 +00:00
parent 732291c4fa
commit 7faa313f05
2 changed files with 5 additions and 9 deletions
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8
arch/arm64/include/asm/assembler.h
View file

@ -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_\@ :

6
arch/arm64/kernel/entry.S
View file

@ -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