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>

2 files changed, 16 insertions, 24 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 670d1343f914..6a5edea2d70b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -177,7 +177,7 @@ struct mpage_da_data {
 
 struct ext4_io_page {
         struct page     *p_page;
-        int             p_count;
+        atomic_t        p_count;
 };
 
 #define MAX_IO_PAGES 128
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index a24c8cca7370..7f5451cd1d38 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -67,6 +67,15 @@ void ext4_ioend_wait(struct inode *inode)
         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 @@ void ext4_free_io_end(ext4_io_end_t *io)
         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 @@ static void ext4_end_bio(struct bio *bio, int error)
                         } 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 @@ submit_and_retry:
         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 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
                 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 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
          * 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;
 }