ext4: fix potential race when freeing ext4_io_page structures
Use an atomic_t and make sure we don't free the structure while we
might still be submitting I/O for that page.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index a24c8cc..7f5451c 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -67,6 +67,15 @@
wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
}
+static void put_io_page(struct ext4_io_page *io_page)
+{
+ if (atomic_dec_and_test(&io_page->p_count)) {
+ end_page_writeback(io_page->p_page);
+ put_page(io_page->p_page);
+ kmem_cache_free(io_page_cachep, io_page);
+ }
+}
+
void ext4_free_io_end(ext4_io_end_t *io)
{
int i;
@@ -75,15 +84,8 @@
BUG_ON(!io);
if (io->page)
put_page(io->page);
- for (i = 0; i < io->num_io_pages; i++) {
- if (--io->pages[i]->p_count == 0) {
- struct page *page = io->pages[i]->p_page;
-
- end_page_writeback(page);
- put_page(page);
- kmem_cache_free(io_page_cachep, io->pages[i]);
- }
- }
+ for (i = 0; i < io->num_io_pages; i++)
+ put_io_page(io->pages[i]);
io->num_io_pages = 0;
wq = to_ioend_wq(io->inode);
if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count) &&
@@ -235,13 +237,7 @@
} while (bh != head);
}
- if (--io_end->pages[i]->p_count == 0) {
- struct page *page = io_end->pages[i]->p_page;
-
- end_page_writeback(page);
- put_page(page);
- kmem_cache_free(io_page_cachep, io_end->pages[i]);
- }
+ put_io_page(io_end->pages[i]);
/*
* If this is a partial write which happened to make
@@ -369,7 +365,7 @@
if ((io_end->num_io_pages == 0) ||
(io_end->pages[io_end->num_io_pages-1] != io_page)) {
io_end->pages[io_end->num_io_pages++] = io_page;
- io_page->p_count++;
+ atomic_inc(&io_page->p_count);
}
return 0;
}
@@ -398,7 +394,7 @@
return -ENOMEM;
}
io_page->p_page = page;
- io_page->p_count = 0;
+ atomic_set(&io_page->p_count, 1);
get_page(page);
for (bh = head = page_buffers(page), block_start = 0;
@@ -430,10 +426,6 @@
* PageWriteback bit from the page to prevent the system from
* wedging later on.
*/
- if (io_page->p_count == 0) {
- put_page(page);
- end_page_writeback(page);
- kmem_cache_free(io_page_cachep, io_page);
- }
+ put_io_page(io_page);
return ret;
}