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    Subject[PATCH 07/36] aio: add delayed cancel support
    Date
    The upcoming aio poll support would like to be able to complete the
    iocb inline from the cancellation context, but that would cause
    a lock order reversal. Add support for optionally moving the cancelation
    outside the context lock to avoid this reversal.

    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Acked-by: Jeff Moyer <jmoyer@redhat.com>
    ---
    fs/aio.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
    1 file changed, 38 insertions(+), 11 deletions(-)

    diff --git a/fs/aio.c b/fs/aio.c
    index 0b6394b4e528..9d7d6e4cde87 100644
    --- a/fs/aio.c
    +++ b/fs/aio.c
    @@ -170,6 +170,10 @@ struct aio_kiocb {
    struct list_head ki_list; /* the aio core uses this
    * for cancellation */

    + unsigned int flags; /* protected by ctx->ctx_lock */
    +#define AIO_IOCB_DELAYED_CANCEL (1 << 0)
    +#define AIO_IOCB_CANCELLED (1 << 1)
    +
    /*
    * If the aio_resfd field of the userspace iocb is not zero,
    * this is the underlying eventfd context to deliver events to.
    @@ -536,9 +540,9 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
    #define AIO_EVENTS_FIRST_PAGE ((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
    #define AIO_EVENTS_OFFSET (AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)

    -void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
    +static void __kiocb_set_cancel_fn(struct aio_kiocb *req,
    + kiocb_cancel_fn *cancel, unsigned int iocb_flags)
    {
    - struct aio_kiocb *req = container_of(iocb, struct aio_kiocb, rw);
    struct kioctx *ctx = req->ki_ctx;
    unsigned long flags;

    @@ -548,8 +552,15 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
    spin_lock_irqsave(&ctx->ctx_lock, flags);
    list_add_tail(&req->ki_list, &ctx->active_reqs);
    req->ki_cancel = cancel;
    + req->flags |= iocb_flags;
    spin_unlock_irqrestore(&ctx->ctx_lock, flags);
    }
    +
    +void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
    +{
    + return __kiocb_set_cancel_fn(container_of(iocb, struct aio_kiocb, rw),
    + cancel, 0);
    +}
    EXPORT_SYMBOL(kiocb_set_cancel_fn);

    /*
    @@ -603,17 +614,27 @@ static void free_ioctx_users(struct percpu_ref *ref)
    {
    struct kioctx *ctx = container_of(ref, struct kioctx, users);
    struct aio_kiocb *req;
    + LIST_HEAD(list);

    spin_lock_irq(&ctx->ctx_lock);
    -
    while (!list_empty(&ctx->active_reqs)) {
    req = list_first_entry(&ctx->active_reqs,
    struct aio_kiocb, ki_list);
    - kiocb_cancel(req);
    - }

    + if (req->flags & AIO_IOCB_DELAYED_CANCEL) {
    + req->flags |= AIO_IOCB_CANCELLED;
    + list_move_tail(&req->ki_list, &list);
    + } else {
    + kiocb_cancel(req);
    + }
    + }
    spin_unlock_irq(&ctx->ctx_lock);

    + while (!list_empty(&list)) {
    + req = list_first_entry(&list, struct aio_kiocb, ki_list);
    + kiocb_cancel(req);
    + }
    +
    percpu_ref_kill(&ctx->reqs);
    percpu_ref_put(&ctx->reqs);
    }
    @@ -1785,15 +1806,22 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
    if (unlikely(!ctx))
    return -EINVAL;

    - spin_lock_irq(&ctx->ctx_lock);
    + ret = -EINVAL;

    + spin_lock_irq(&ctx->ctx_lock);
    kiocb = lookup_kiocb(ctx, iocb, key);
    + if (kiocb) {
    + if (kiocb->flags & AIO_IOCB_DELAYED_CANCEL) {
    + kiocb->flags |= AIO_IOCB_CANCELLED;
    + } else {
    + ret = kiocb_cancel(kiocb);
    + kiocb = NULL;
    + }
    + }
    + spin_unlock_irq(&ctx->ctx_lock);
    +
    if (kiocb)
    ret = kiocb_cancel(kiocb);
    - else
    - ret = -EINVAL;
    -
    - spin_unlock_irq(&ctx->ctx_lock);

    if (!ret) {
    /*
    @@ -1805,7 +1833,6 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
    }

    percpu_ref_put(&ctx->users);
    -
    return ret;
    }

    --
    2.14.2
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