[PATCH] Btrfs: cleanup pages properly when ENOMEM in compression

[PATCH] Btrfs: cleanup pages properly when ENOMEM in compression

[Josef Bacik]

We were freeing non-existent pages which was causing a panic for a user who
was suffering from ENOMEM.  This patch fixes the problem.  Thanks,

Reported-by: Jérôme Poulin <jeromepoulin@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
---
 fs/btrfs/compression.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 43d1c5a..36eb5f2 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -577,6 +577,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	u64 em_start;
 	struct extent_map *em;
 	int ret = -ENOMEM;
+	int faili = 0;
 	u32 *sums;
 
 	tree = &BTRFS_I(inode)->io_tree;
@@ -626,8 +627,11 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
 		cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
 							      __GFP_HIGHMEM);
-		if (!cb->compressed_pages[pg_index])
+		if (!cb->compressed_pages[pg_index]) {
+			faili = pg_index - 1;
+			ret = -ENOMEM;
 			goto fail2;
+		}
 	}
 	cb->nr_pages = nr_pages;
 
@@ -713,8 +717,10 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	return 0;
 
 fail2:
-	for (pg_index = 0; pg_index < nr_pages; pg_index++)
-		free_page((unsigned long)cb->compressed_pages[pg_index]);
+	while (faili >= 0) {
+		__free_page(cb->compressed_pages[pg_index]);
+		faili--;
+	}
 
 	kfree(cb->compressed_pages);
 fail1:
-- 
1.7.7.6

Re: [PATCH] Btrfs: cleanup pages properly when ENOMEM in compression

[David Sterba]

On Fri, Oct 05, 2012 at 01:49:19PM -0400, Josef Bacik wrote:
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -577,6 +577,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>  	u64 em_start;
>  	struct extent_map *em;
>  	int ret = -ENOMEM;
> +	int faili = 0;
>  	u32 *sums;
>  
>  	tree = &BTRFS_I(inode)->io_tree;
> @@ -626,8 +627,11 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>  	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
>  		cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
>  							      __GFP_HIGHMEM);
> -		if (!cb->compressed_pages[pg_index])
> +		if (!cb->compressed_pages[pg_index]) {
> +			faili = pg_index - 1;
> +			ret = -ENOMEM;
>  			goto fail2;
> +		}
>  	}
>  	cb->nr_pages = nr_pages;
>  
> @@ -713,8 +717,10 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>  	return 0;
>  
>  fail2:
> -	for (pg_index = 0; pg_index < nr_pages; pg_index++)
> -		free_page((unsigned long)cb->compressed_pages[pg_index]);
> +	while (faili >= 0) {
> +		__free_page(cb->compressed_pages[pg_index]);
                                                 ^^^^^^^^

s/pg_index/faili/

Also, faili (how do you pronounce that?) is initialized to 0, the while
loop will always fire (and burn a page), initialize it to -1.

Other than that, I like the fix, thanks.

> +		faili--;
> +	}
>  
>  	kfree(cb->compressed_pages);
>  fail1:

david

Re: [PATCH] Btrfs: cleanup pages properly when ENOMEM in compression

[David Sterba]

On Fri, Oct 05, 2012 at 10:06:17PM +0200, David Sterba wrote:
> Also, faili (how do you pronounce that?) is initialized to 0, the while
> loop will always fire (and burn a page), initialize it to -1.

My oversight sorry, it takes a different codepath and this will not
happen.

david