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Date: Thu, 19 Dec 2013 15:31:11 -0500
From: Benjamin LaHaise <bcrl@...ck.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kent Overstreet <kmo@...erainc.com>, Dave Jones <davej@...hat.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>, Christoph Lameter <cl@...two.org>,
Al Viro <viro@...iv.linux.org.uk>
Subject: Re: bad page state in 3.13-rc4
On Fri, Dec 20, 2013 at 05:11:12AM +0900, Linus Torvalds wrote:
> On Fri, Dec 20, 2013 at 5:02 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Why not just get rid of the idiotic get_user_pages() crap then?
> > Something like the attached patch?
> >
> > Totally untested, but at least it makes *some* amount of sense.
>
> Ok, that can't work, since the ring_pages[] allocation happens later.
> So that part needs to be moved up, and it needs to initialize
> 'nr_pages'.
>
> So here's the same patch, but with stuff moved around a bit, and the
> "oops, couldn't create page" part fixed.
>
> Bit it's still totally and entirely untested.
That looks much better. I think the following is also needed to nail down
the migratepage operation as well. I'll give these two a few tests
together.
-ben
--
"Thought is the essence of where you are now."
diff --git a/fs/aio.c b/fs/aio.c
index 6efb7f6..eec0ae4 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -244,8 +244,13 @@ static void aio_free_ring(struct kioctx *ctx)
int i;
for (i = 0; i < ctx->nr_pages; i++) {
+ struct page *page;
pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
page_count(ctx->ring_pages[i]));
+ page = ctx->ring_pages[i];
+ if (!page)
+ continue;
+ ctx->ring_pages[i] = NULL;
put_page(ctx->ring_pages[i]);
}
@@ -280,18 +285,42 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
unsigned long flags;
int rc;
+ /* Serialize access to the old page */
+ if (!trylock_page(old))
+ return -EAGAIN;
+
+ rc = 0;
+
+ spin_lock(&mapping->private_lock);
+ ctx = mapping->private_data;
+ if (ctx) {
+ pgoff_t idx;
+ spin_lock_irqsave(&ctx->completion_lock, flags);
+ idx = old->index;
+ if (idx < (pgoff_t)ctx->nr_pages) {
+ if (ctx->ring_pages[idx] != old)
+ rc = -EAGAIN;
+ } else
+ rc = -EINVAL;
+ spin_unlock_irqrestore(&ctx->completion_lock, flags);
+ } else
+ rc = -EINVAL;
+ spin_unlock(&mapping->private_lock);
+
+ if (rc != 0)
+ return rc;
+
/* Writeback must be complete */
BUG_ON(PageWriteback(old));
- put_page(old);
+ get_page(new);
- rc = migrate_page_move_mapping(mapping, new, old, NULL, mode);
+ rc = migrate_page_move_mapping(mapping, new, old, NULL, mode, 1);
if (rc != MIGRATEPAGE_SUCCESS) {
- get_page(old);
+ unlock_page(old);
+ put_page(new);
return rc;
}
- get_page(new);
-
/* We can potentially race against kioctx teardown here. Use the
* address_space's private data lock to protect the mapping's
* private_data.
@@ -305,10 +334,16 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
idx = old->index;
if (idx < (pgoff_t)ctx->nr_pages)
ctx->ring_pages[idx] = new;
+ else
+ rc = -EINVAL;
spin_unlock_irqrestore(&ctx->completion_lock, flags);
} else
rc = -EBUSY;
spin_unlock(&mapping->private_lock);
+ unlock_page(old);
+
+ if (rc == MIGRATEPAGE_SUCCESS)
+ put_page(old);
return rc;
}
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index b7717d7..f015c05 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -55,7 +55,8 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page);
extern int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
- struct buffer_head *head, enum migrate_mode mode);
+ struct buffer_head *head, enum migrate_mode mode,
+ int extra_count);
#else
static inline void putback_lru_pages(struct list_head *l) {}
diff --git a/mm/migrate.c b/mm/migrate.c
index e9b7102..e73823e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -317,14 +317,15 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
*/
int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
- struct buffer_head *head, enum migrate_mode mode)
+ struct buffer_head *head, enum migrate_mode mode,
+ int extra_count)
{
int expected_count = 0;
void **pslot;
if (!mapping) {
/* Anonymous page without mapping */
- if (page_count(page) != 1)
+ if (page_count(page) != (expected_count + 1))
return -EAGAIN;
return MIGRATEPAGE_SUCCESS;
}
@@ -584,7 +585,7 @@ int migrate_page(struct address_space *mapping,
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
- rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
+ rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
@@ -611,7 +612,7 @@ int buffer_migrate_page(struct address_space *mapping,
head = page_buffers(page);
- rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
+ rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
--
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