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SubjectRe: [PATCH] block: avoid infinite loop in get_task_io_context()
Hello, Eric, Jens.

On Thu, May 31, 2012 at 12:38:26PM +0200, Eric Dumazet wrote:
> [PATCH] block: avoid infinite loop in get_task_io_context()
>
> Calling get_task_io_context() on a exiting task which isn't %current can
> loop forever. This triggers at boot time on my dev machine.
>
> BUG: soft lockup - CPU#3 stuck for 22s ! [mountall.1603]
>
> Fix this by making create_task_io_context() returns -EBUSY in this case
> to break the loop.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alan Cox <alan@linux.intel.com>
> ---
> block/blk-ioc.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-ioc.c b/block/blk-ioc.c
> index 1e2d53b..893b800 100644
> --- a/block/blk-ioc.c
> +++ b/block/blk-ioc.c
> @@ -235,6 +235,7 @@ void ioc_clear_queue(struct request_queue *q)
> int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
> {
> struct io_context *ioc;
> + int ret;
>
> ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
> node);
> @@ -262,9 +263,12 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
> task->io_context = ioc;
> else
> kmem_cache_free(iocontext_cachep, ioc);
> +
> + ret = task->io_context ? 0 : -EBUSY;
> +
> task_unlock(task);
>
> - return 0;
> + return ret;

Ah, right. This seems correct to me.

FWIW-late-Acked-by: Tejun Heo <tj@kernel.org>

Thanks. :)

--
tejun


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