On Wed, 21 Mar 2001, Linus Torvalds wrote:
>
> The deadlock implies that somebody scheduled with page_table_lock held.
> Which would be really bad.
..and it is probably do_swap_page().
Despite the name, "lookup_swap_cache()" does more than a lookup - it will
wait for the page that it looked up. And we call it with the
page_table_lock held in do_swap_page().
Ho humm. Does the appended patch fix it for you? Looks obvious enough, but
this bug is actually hidden on true SMP, and I'm too lazy to test with
"num_cpus=1" or something..
Linus
-----
diff -u --recursive --new-file pre6/linux/mm/memory.c linux/mm/memory.c
--- pre6/linux/mm/memory.c Tue Mar 20 23:13:03 2001
+++ linux/mm/memory.c Wed Mar 21 22:21:27 2001
@@ -1031,18 +1031,20 @@
struct vm_area_struct * vma, unsigned long address,
pte_t * page_table, swp_entry_t entry, int write_access)
{
- struct page *page = lookup_swap_cache(entry);
+ struct page *page;
pte_t pte;
+ spin_unlock(&mm->page_table_lock);
+ page = lookup_swap_cache(entry);
if (!page) {
- spin_unlock(&mm->page_table_lock);
lock_kernel();
swapin_readahead(entry);
page = read_swap_cache(entry);
unlock_kernel();
- spin_lock(&mm->page_table_lock);
- if (!page)
+ if (!page) {
+ spin_lock(&mm->page_table_lock);
return -1;
+ }
flush_page_to_ram(page);
flush_icache_page(vma, page);
@@ -1053,13 +1055,13 @@
* Must lock page before transferring our swap count to already
* obtained page count.
*/
- spin_unlock(&mm->page_table_lock);
lock_page(page);
- spin_lock(&mm->page_table_lock);
/*
- * Back out if somebody else faulted in this pte while we slept.
+ * Back out if somebody else faulted in this pte while we
+ * released the page table lock.
*/
+ spin_lock(&mm->page_table_lock);
if (pte_present(*page_table)) {
UnlockPage(page);
page_cache_release(page);
-
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:16 EST