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Subject[PATCH 4.14 66/75] powerpc/kprobes: Disable preemption before invoking probe handler for optprobes
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

commit 8a2d71a3f2737e2448aa68de2b6052cb570d3d2a upstream.

Per Documentation/kprobes.txt, probe handlers need to be invoked with
preemption disabled. Update optimized_callback() to do so. Also move
get_kprobe_ctlblk() invocation post preemption disable, since it
accesses pre-cpu data.

This was not an issue so far since optprobes wasn't selected if
CONFIG_PREEMPT was enabled. Commit a30b85df7d599f ("kprobes: Use
synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y") changes
this.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kernel/optprobes.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/powerpc/kernel/optprobes.c
+++ b/arch/powerpc/kernel/optprobes.c
@@ -115,7 +115,6 @@ static unsigned long can_optimize(struct
static void optimized_callback(struct optimized_kprobe *op,
struct pt_regs *regs)
{
- struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
unsigned long flags;

/* This is possible if op is under delayed unoptimizing */
@@ -124,13 +123,14 @@ static void optimized_callback(struct op

local_irq_save(flags);
hard_irq_disable();
+ preempt_disable();

if (kprobe_running()) {
kprobes_inc_nmissed_count(&op->kp);
} else {
__this_cpu_write(current_kprobe, &op->kp);
regs->nip = (unsigned long)op->kp.addr;
- kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+ get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
opt_pre_handler(&op->kp, regs);
__this_cpu_write(current_kprobe, NULL);
}
@@ -140,6 +140,7 @@ static void optimized_callback(struct op
* local_irq_restore() will re-enable interrupts,
* if they were hard disabled.
*/
+ preempt_enable_no_resched();
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(optimized_callback);

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