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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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