> -----Original Message-----
> From: linux-rdma-owner@xxxxxxxxxxxxxxx <linux-rdma-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Leon Romanovsky
> Sent: Wednesday, October 2, 2019 7:33 AM
> To: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe
> <jgg@xxxxxxxxxxxx>
> Cc: Leon Romanovsky <leonro@xxxxxxxxxxxx>; RDMA mailing list <linux-
> rdma@xxxxxxxxxxxxxxx>
> Subject: [PATCH rdma-next 2/2] RDMA/core: Check that process is still alive
> before sending it to the users
>
> From: Leon Romanovsky <leonro@xxxxxxxxxxxx>
>
> The PID information can disappear asynchronically because task can be killed
> and moved to zombie state. In such case, PID will be zero in similar way to the
> kernel tasks. Recognize such situation where we are asking to return orphaned
> object and simply skip filling PID attribute.
>
> As part of this change, document the same scenario in counter.c code.
>
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
> ---
> drivers/infiniband/core/counters.c | 14 ++++++++++++--
> drivers/infiniband/core/nldev.c | 31 ++++++++++++++++++++++--------
> 2 files changed, 35 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/infiniband/core/counters.c
> b/drivers/infiniband/core/counters.c
> index 12ba2685abcf..47c551a0bcb0 100644
> --- a/drivers/infiniband/core/counters.c
> +++ b/drivers/infiniband/core/counters.c
> @@ -149,8 +149,18 @@ static bool auto_mode_match(struct ib_qp *qp, struct
> rdma_counter *counter,
> struct auto_mode_param *param = &counter->mode.param;
> bool match = true;
>
> - /* Ensure that counter belongs to the right PID */
> - if (task_pid_nr(counter->res.task) != task_pid_nr(qp->res.task))
> + /*
> + * Ensure that counter belongs to the right PID.
> + * This operation can race with user space which kills
> + * the process and leaves QP and counters orphans.
> + *
> + * It is not a big deal because exitted task will leave both
> + * QP and counter in the same bucket of zombie process. Just ensure
> + * that process is still alive before procedding.
> + *
> + */
> + if (task_pid_nr(counter->res.task) != task_pid_nr(qp->res.task) ||
> + !task_pid_nr(qp->res.task))
> return false;
>
> if (auto_mask & RDMA_COUNTER_MASK_QP_TYPE) diff --git
> a/drivers/infiniband/core/nldev.c b/drivers/infiniband/core/nldev.c index
> 71bc08510064..c6fe0c52f6dc 100644
> --- a/drivers/infiniband/core/nldev.c
> +++ b/drivers/infiniband/core/nldev.c
> @@ -399,20 +399,35 @@ static int fill_res_info(struct sk_buff *msg, struct
> ib_device *device) static int fill_res_name_pid(struct sk_buff *msg,
> struct rdma_restrack_entry *res) {
> + int err = 0;
> + pid_t pid;
> +
> /*
> * For user resources, user is should read /proc/PID/comm to get the
> * name of the task file.
> */
> if (rdma_is_kernel_res(res)) {
> - if (nla_put_string(msg,
> RDMA_NLDEV_ATTR_RES_KERN_NAME,
> - res->kern_name))
> - return -EMSGSIZE;
> - } else {
> - if (nla_put_u32(msg, RDMA_NLDEV_ATTR_RES_PID,
> - task_pid_vnr(res->task)))
> - return -EMSGSIZE;
> + err = nla_put_string(msg,
> RDMA_NLDEV_ATTR_RES_KERN_NAME,
> + res->kern_name);
> + goto out;
> }
> - return 0;
> +
> + pid = task_pid_vnr(res->task);
> + /*
> + * PID == 0 returns in two scenarios:
> + * 1. It is kernel task, but because we checked above, it won't be
> possible.
Please drop above comment point 1. See more below.
> + * 2. Task is dead and in zombie state. There is no need to print PID
> anymore.
> + */
> + if (pid)
> + /*
> + * This part is racy, task can be killed and PID will be zero right
> + * here but it is ok, next query won't return PID. We don't
> promise
> + * real-time reflection of SW objects.
> + */
> + err = nla_put_u32(msg, RDMA_NLDEV_ATTR_RES_PID, pid);
> +
> +out:
> + return err ? -EMSGSIZE : 0;
> }
Below code reads better along with rest of the comments in the patch.
if (kern_resource) {
err = nla_put_string(msg, RDMA_NLDEV_ATTR_RES_KERN_NAME,
res->kern_name);
} else {
pid_t pid;
pid = task_pid_vnr(res->task);
if (pid)
err = nla_put_u32(msg, RDMA_NLDEV_ATTR_RES_PID, pid);
}
>
> static bool fill_res_entry(struct ib_device *dev, struct sk_buff *msg,
> --
> 2.20.1
