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    Subject[PATCH 5/9] block: ioc_task_link() can't fail
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    ioc_task_link() is used to share %current's ioc on clone.  If
    %current->is_context is set, %current is guaranteed to have refcount
    on the ioc and, thus, ioc_task_link() can't fail.

    Replace error checking in ioc_task_link() with WARN_ON_ONCE() and make
    it just increment refcount and nr_tasks.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    ---
    include/linux/iocontext.h | 16 +++++-----------
    kernel/fork.c | 5 ++---
    2 files changed, 7 insertions(+), 14 deletions(-)

    diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
    index 1a30180..81a8870 100644
    --- a/include/linux/iocontext.h
    +++ b/include/linux/iocontext.h
    @@ -120,18 +120,12 @@ struct io_context {
    struct work_struct release_work;
    };

    -static inline struct io_context *ioc_task_link(struct io_context *ioc)
    +static inline void ioc_task_link(struct io_context *ioc)
    {
    - /*
    - * if ref count is zero, don't allow sharing (ioc is going away, it's
    - * a race).
    - */
    - if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
    - atomic_inc(&ioc->nr_tasks);
    - return ioc;
    - }
    -
    - return NULL;
    + WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
    + WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
    + atomic_long_inc(&ioc->refcount);
    + atomic_inc(&ioc->nr_tasks);
    }

    struct task_struct;
    diff --git a/kernel/fork.c b/kernel/fork.c
    index b77fd55..a1b6327 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -901,9 +901,8 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
    * Share io context with parent, if CLONE_IO is set
    */
    if (clone_flags & CLONE_IO) {
    - tsk->io_context = ioc_task_link(ioc);
    - if (unlikely(!tsk->io_context))
    - return -ENOMEM;
    + ioc_task_link(ioc);
    + tsk->io_context = ioc;
    } else if (ioprio_valid(ioc->ioprio)) {
    new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
    if (unlikely(!new_ioc))
    --
    1.7.7.3


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