FAILED: patch "[PATCH] x86/speculation: Prevent deadlock on ssb_state::lock" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2f5fb19341883bb6e37da351bc3700489d8506a7 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <[email protected]>
Date: Sun, 14 Apr 2019 19:51:06 +0200
Subject: [PATCH] x86/speculation: Prevent deadlock on ssb_state::lock

Mikhail reported a lockdep splat related to the AMD specific ssb_state lock:

  CPU0                       CPU1
  lock(&st->lock);
                             local_irq_disable();
                             lock(&(&sighand->siglock)->rlock);
                             lock(&st->lock);
  <Interrupt>
     lock(&(&sighand->siglock)->rlock);

*** DEADLOCK ***

The connection between sighand->siglock and st->lock comes through seccomp, which takes st->lock while holding sighand->siglock.

Make sure interrupts are disabled when __speculation_ctrl_update() is invoked via prctl() -> speculation_ctrl_update(). Add a lockdep assert to catch future offenders.

index 58ac7be52c7a..957eae13b370 100644
@@ -426,6 +426,8 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
 	u64 msr = x86_spec_ctrl_base;
 	bool updmsr = false;
 
+	lockdep_assert_irqs_disabled();
+
 	/*
 	 * If TIF_SSBD is different, select the proper mitigation
 	 * method. Note that if SSBD mitigation is disabled or permanentely

@@ -477,10 +479,12 @@ static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
 
 void speculation_ctrl_update(unsigned long tif)
 {
+	unsigned long flags;
+
 	/* Forced update. Make sure all relevant TIF flags are different */
-	preempt_disable();
+	local_irq_save(flags);
 	__speculation_ctrl_update(~tif, tif);
-	preempt_enable();
+	local_irq_restore(flags);
 }
 
 /* Called from seccomp/prctl update */