Commit dfa75863 authored Jun 29, 2018 by Eric Farman Committed by Martin Schwidefsky Jul 02, 2018

s390/mm: fix refcount usage for 4K pgste



s390 no longer uses the _mapcount field in struct page to identify
the page table format being used. While the code was diligent in handling
the different mappings, it neglected to turn "off" the map bits when
alloc_pgste was being used. This resulted in bits remaining "on" in the
_refcount field, and thus an artifically huge "in use" count that prevents
the pages from actually being released by __free_page.

There's opportunity for improvement in the "1 vs 3" vs "1U vs 3U" vs
"0x1 vs 0x11" etc. variations for all these calls, I am just keeping
things simple compared to neighboring code.

Fixes: 620b4e90 ("s390: use _refcount for pgtables")
Reported-by: Halil Pasic <pasic@linux.ibm.com>
Bisected-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 3284da34

arch/s390/mm/pgalloc.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -252,6 +252,8 @@ void page_table_free(struct mm_struct mm, unsigned long table)
		spin_unlock_bh(&mm->context.lock);
		if (mask != 0)
		return;
		} else {
		atomic_xor_bits(&page->_refcount, 3U << 24);
		}

		pgtable_page_dtor(page);
		@@ -304,6 +306,8 @@ static void __tlb_remove_table(void *_table)
		break;
		/* fallthrough */
		case 3: /* 4K page table with pgstes */
		if (mask & 3)
		atomic_xor_bits(&page->_refcount, 3 << 24);
		pgtable_page_dtor(page);
		__free_page(page);
		break;

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