[PATCH 4.2.y-ckt 104/206] MIPS: Disable preemption during prctl(PR_SET_FP_MODE, ...)

[Kamal Mostafa]

4.2.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Paul Burton <paul.burton at imgtec.com>

commit bd239f1e1429e7781096bf3884bdb1b2b1bb4f28 upstream.

Whilst a PR_SET_FP_MODE prctl is performed there are decisions made
based upon whether the task is executing on the current CPU. This may
change if we're preempted, so disable preemption to avoid such changes
for the lifetime of the mode switch.

Signed-off-by: Paul Burton <paul.burton at imgtec.com>
Fixes: 9791554b45a2 ("MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS")
Reviewed-by: Maciej W. Rozycki <macro at imgtec.com>
Tested-by: Aurelien Jarno <aurelien at aurel32.net>
Cc: Adam Buchbinder <adam.buchbinder at gmail.com>
Cc: James Hogan <james.hogan at imgtec.com>
Cc: linux-mips at linux-mips.org
Cc: linux-kernel at vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13144/
Signed-off-by: Ralf Baechle <ralf at linux-mips.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/mips/kernel/process.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 6b3ae73..89847be 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -603,6 +603,9 @@ int mips_set_process_fp_mode(struct task_struct *task, unsigned int value)
 	if (!(value & PR_FP_MODE_FR) && cpu_has_fpu && cpu_has_mips_r6)
 		return -EOPNOTSUPP;
 
+	/* Proceed with the mode switch */
+	preempt_disable();
+
 	/* Save FP & vector context, then disable FPU & MSA */
 	if (task->signal == current->signal)
 		lose_fpu(1);
@@ -661,6 +664,7 @@ int mips_set_process_fp_mode(struct task_struct *task, unsigned int value)
 
 	/* Allow threads to use FP again */
 	atomic_set(&task->mm->context.fp_mode_switching, 0);
+	preempt_enable();
 
 	return 0;
 }
-- 
2.7.4