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Subject[PATCH] rmap deadlock
zap_pte_range's page_remove_rmap spins for pte_chain_lock while holding
pte_page_lock; while kswapd's try_to_unmap_one spins for pte_page_lock
while holding pte_chain_lock. This is well documented, and was handled
before by a trylock in try_to_unmap_one: add pte_chain_trylock and use
its alias pte_page_trylock here; and update those comments.

--- 2.5.42-mm3/include/linux/rmap-locking.h Tue Oct 15 06:43:41 2002
+++ linux/include/linux/rmap-locking.h Tue Oct 15 13:14:35 2002
@@ -23,6 +23,18 @@
#endif
}

+static inline int pte_chain_trylock(struct page *page)
+{
+ preempt_disable();
+#ifdef CONFIG_SMP
+ if (test_and_set_bit(PG_chainlock, &page->flags)) {
+ preempt_enable();
+ return 0;
+ }
+#endif
+ return 1;
+}
+
static inline void pte_chain_unlock(struct page *page)
{
#ifdef CONFIG_SMP
@@ -32,5 +44,6 @@
preempt_enable();
}

-#define pte_page_lock pte_chain_lock
-#define pte_page_unlock pte_chain_unlock
+#define pte_page_lock pte_chain_lock
+#define pte_page_trylock pte_chain_trylock
+#define pte_page_unlock pte_chain_unlock
--- 2.5.42-mm3/mm/rmap.c Tue Oct 15 06:43:41 2002
+++ linux/mm/rmap.c Tue Oct 15 13:14:35 2002
@@ -14,11 +14,11 @@
/*
* Locking:
* - the page->pte.chain is protected by the PG_chainlock bit,
- * which nests within the zone->lru_lock, then the
- * mm->page_table_lock, and then the page lock.
+ * which nests within the zone->lru_lock, then the pte_page_lock,
+ * and then the page lock.
* - because swapout locking is opposite to the locking order
* in the page fault path, the swapout path uses trylocks
- * on the mm->page_table_lock
+ * on the pte_page_lock.
*/
#include <linux/mm.h>
#include <linux/pagemap.h>
@@ -280,7 +280,7 @@
* @ptep: the page table entry mapping this page
*
* Add a new pte reverse mapping to a page.
- * The caller needs to hold the mm->page_table_lock.
+ * The caller needs to hold the pte_page_lock.
*/
void page_add_rmap(struct page * page, pte_t * ptep)
{
@@ -377,7 +377,7 @@
* Removes the reverse mapping from the pte_chain of the page,
* after that the caller can clear the page table entry and free
* the page.
- * Caller needs to hold the mm->page_table_lock.
+ * Caller needs to hold the pte_page_lock.
*/
void page_remove_rmap(struct page * page, pte_t * ptep)
{
@@ -560,7 +560,7 @@
* zone->lru_lock page_launder()
* page lock page_launder(), trylock
* pte_chain_lock page_launder()
- * mm->page_table_lock try_to_unmap_one(), trylock
+ * pte_page_lock try_to_unmap_one(), trylock
*/
static int FASTCALL(try_to_unmap_one(struct page *, pte_addr_t));
static int try_to_unmap_one(struct page * page, pte_addr_t paddr)
@@ -571,7 +571,10 @@
unsigned long address = ptep_to_address(ptep);
int ret;

- pte_page_lock(ptepage);
+ if (!pte_page_trylock(ptepage)) {
+ rmap_ptep_unmap(ptep);
+ return SWAP_AGAIN;
+ }

ret = pgtable_check_mlocked(ptepage, address);
if (ret != SWAP_SUCCESS)
-
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