Patch "parisc: Fix race in pci-dma.c" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

parisc: Fix race in pci-dma.c

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
parisc-fix-race-in-pci-dma.c.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: John David Anglin <[email protected]>
Date: Thu, 24 Nov 2016 20:06:32 -0500
Subject: parisc: Fix race in pci-dma.c

From: John David Anglin <[email protected]>

commit c0452fb9fb8f49c7d68ab9fa0ad092016be7b45f upstream.

We are still troubled by occasional random segmentation faults and memory memory corruption on SMP machines. The causes quite a few package builds to fail on the Debian buildd machines for parisc. When gcc-6 failed to build three times in a row, I looked again at the TLB related code. I found a couple of issues. This is the first.

In general, we need to ensure page table updates and corresponding TLB purges are atomic. The attached patch fixes an instance in pci-dma.c where the page table update was not guarded by the TLB lock.

Tested on rp3440 and c8000. So far, no further random segmentation faults have been observed.

---
 arch/parisc/kernel/pci-dma.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -95,8 +95,8 @@ static inline int map_pte_uncached(pte_t
 
 		if (!pte_none(*pte))
 			printk(KERN_ERR "map_pte_uncached: page already exists\n");
-		set_pte(pte, __mk_pte(*paddr_ptr, PAGE_KERNEL_UNC));
 		purge_tlb_start(flags);
+		set_pte(pte, __mk_pte(*paddr_ptr, PAGE_KERNEL_UNC));
 		pdtlb_kernel(orig_vaddr);
 		purge_tlb_end(flags);
 		vaddr += PAGE_SIZE;

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/parisc-fix-race-in-pci-dma.c.patch queue-4.8/parisc-also-flush-data-tlb-in-flush_icache_page_asm.patch queue-4.8/parisc-fix-races-in-parisc_setup_cache_timing.patch