[PATCH 1/2] aio: correct calculation of available events

[PATCH 1/2] aio: correct calculation of available events

[Benjamin LaHaise]

When the number of available events in the ring buffer is calculated,
the avail calculation is incorrect when head == tail.  This is harmless
in aio_read_events_ring(), but in free_ioctx() leads to the subsequent
WARN_ON(atomic_read(&ctx->reqs_available) > ctx->nr).  Correct this.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
---
 fs/aio.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 24ba228..dc52b0c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -337,7 +337,8 @@ static void free_ioctx(struct kioctx *ctx)
 	while (atomic_read(&ctx->reqs_available) < ctx->nr) {
 		wait_event(ctx->wait, head != ctx->shadow_tail);
 
-		avail = (head < ctx->shadow_tail ? ctx->shadow_tail : ctx->nr) - head;
+		avail = (head <= ctx->shadow_tail ?
+			 ctx->shadow_tail : ctx->nr) - head;
 
 		atomic_add(avail, &ctx->reqs_available);
 		head += avail;
@@ -884,7 +885,7 @@ static long aio_read_events_ring(struct kioctx *ctx,
 		goto out;
 
 	while (ret < nr) {
-		long avail = (head < ctx->shadow_tail
+		long avail = (head <= ctx->shadow_tail
 			      ? ctx->shadow_tail : ctx->nr) - head;
 		struct io_event *ev;
 		struct page *page;
-- 
1.7.4.1


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Re: [PATCH 1/2] aio: correct calculation of available events

[Kent Overstreet]

On Wed, Feb 13, 2013 at 12:45:52PM -0500, Benjamin LaHaise wrote:
> When the number of available events in the ring buffer is calculated,
> the avail calculation is incorrect when head == tail.  This is harmless
> in aio_read_events_ring(), but in free_ioctx() leads to the subsequent
> WARN_ON(atomic_read(&ctx->reqs_available) > ctx->nr).  Correct this.
> 
> Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
> ---
>  fs/aio.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 24ba228..dc52b0c 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -337,7 +337,8 @@ static void free_ioctx(struct kioctx *ctx)
>  	while (atomic_read(&ctx->reqs_available) < ctx->nr) {
>  		wait_event(ctx->wait, head != ctx->shadow_tail);
>  
> -		avail = (head < ctx->shadow_tail ? ctx->shadow_tail : ctx->nr) - head;
> +		avail = (head <= ctx->shadow_tail ?
> +			 ctx->shadow_tail : ctx->nr) - head;
>  
>  		atomic_add(avail, &ctx->reqs_available);
>  		head += avail;
> @@ -884,7 +885,7 @@ static long aio_read_events_ring(struct kioctx *ctx,
>  		goto out;
>  
>  	while (ret < nr) {
> -		long avail = (head < ctx->shadow_tail
> +		long avail = (head <= ctx->shadow_tail
>  			      ? ctx->shadow_tail : ctx->nr) - head;
>  		struct io_event *ev;
>  		struct page *page;
> -- 
> 1.7.4.1
> 
> 
> -- 
> "Thought is the essence of where you are now."

Whoops!

Reviewed-by: Kent Overstreet <koverstreet@google.com>

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