Re: NMI watchdog: BUG: soft lockup

[David Miller <davem@davemloft.net>]

From: David Miller <davem@davemloft.net>
Date: Tue, 25 Oct 2016 11:22:31 -0400 (EDT)

> From: James Clarke <jrtc27@jrtc27.com>
> Date: Tue, 25 Oct 2016 16:11:52 +0100
> 
>> Yep, that fix is still there, but you will note that end *is* above start in
>> the call. Something is being allocated and freed right at the end of the malloc
>> area, so itʼs iterating over almost the entire thing.
> 
> Ok, let me think about this some more.

So, for the TSB part we don't need to do anything fancy, something like
the patch below will suffice.

As per the TLB flush that's a bit more complicated.

For the older chips we need to do more work because they unfortunately
defined the context flush to even remove locked TLB entries.
Otherwise we could simply do a nucleus context flush if the range is
too large.  So we'll have to use diagnostic accesses to implement the
same functionality.

UltraSPARC-III and later provide more usable facilities for this
situation.  UltraSPARC-III/IV have a "flush all" which removes all
non-locked TLB entries.  And all of the sun4v chips have a more
reasonable context flush, which does not remove "permanent" entries.

I'll start hacking something up.

diff --git a/arch/sparc/mm/tsb.c b/arch/sparc/mm/tsb.c
index f2b7711..1f63411 100644
--- a/arch/sparc/mm/tsb.c
+++ b/arch/sparc/mm/tsb.c
@@ -27,6 +27,20 @@ static inline int tag_compare(unsigned long tag, unsigned long vaddr)
 	return (tag == (vaddr >> 22));
 }
 
+static void flush_tsb_kernel_range_scan(unsigned long start, unsigned long end)
+{
+	unsigned long idx;
+
+	start >> 22;
+	end >> 22;
+	for (idx = 0; idx < KERNEL_TSB_NENTRIES; idx++) {
+		struct tsb *ent = &swapper_tsb[idx];
+
+		if (ent->tag >= start && end->tag < end)
+			ent->tag = (1UL << TSB_TAG_INVALID_BIT);
+	}
+}
+
 /* TSB flushes need only occur on the processor initiating the address
  * space modification, not on each cpu the address space has run on.
  * Only the TLB flush needs that treatment.
@@ -36,6 +50,9 @@ void flush_tsb_kernel_range(unsigned long start, unsigned long end)
 {
 	unsigned long v;
 
+	if ((end - start) >> PAGE_SHIFT >= 2 * KERNEL_TSB_NENTRIES)
+		return flush_tsb_kernel_range_scan(start, end);
+
 	for (v = start; v < end; v += PAGE_SIZE) {
 		unsigned long hash = tsb_hash(v, PAGE_SHIFT,
 					      KERNEL_TSB_NENTRIES);