On Thu, Jul 28, 2016 at 02:16:48AM -0400, Guoqing Jiang wrote:
> When some node leaves cluster, then it's bitmap need to be
> synced by another node, so "md*_recover" thread is triggered
> for the purpose. However, with below steps. we can find tasks
> hang happened either in B or C.
>
> 1. Node A create a resyncing cluster raid1, assemble it in
> other two nodes (B and C).
> 2. stop array in B and C.
> 3. stop array in A.
>
> linux44:~ # ps aux|grep md|grep D
> root 5938 0.0 0.1 19852 1964 pts/0 D+ 14:52 0:00 mdadm -S md0
> root 5939 0.0 0.0 0 0 ? D 14:52 0:00 [md0_recover]
>
> linux44:~ # cat /proc/5939/stack
> [<ffffffffa04cf321>] dlm_lock_sync+0x71/0x90 [md_cluster]
> [<ffffffffa04d0705>] recover_bitmaps+0x125/0x220 [md_cluster]
> [<ffffffffa052105d>] md_thread+0x16d/0x180 [md_mod]
> [<ffffffff8107ad94>] kthread+0xb4/0xc0
> [<ffffffff8152a518>] ret_from_fork+0x58/0x90
>
> linux44:~ # cat /proc/5938/stack
> [<ffffffff8107afde>] kthread_stop+0x6e/0x120
> [<ffffffffa0519da0>] md_unregister_thread+0x40/0x80 [md_mod]
> [<ffffffffa04cfd20>] leave+0x70/0x120 [md_cluster]
> [<ffffffffa0525e24>] md_cluster_stop+0x14/0x30 [md_mod]
> [<ffffffffa05269ab>] bitmap_free+0x14b/0x150 [md_mod]
> [<ffffffffa0523f3b>] do_md_stop+0x35b/0x5a0 [md_mod]
> [<ffffffffa0524e83>] md_ioctl+0x873/0x1590 [md_mod]
> [<ffffffff81288464>] blkdev_ioctl+0x214/0x7d0
> [<ffffffff811dd3dd>] block_ioctl+0x3d/0x40
> [<ffffffff811b92d4>] do_vfs_ioctl+0x2d4/0x4b0
> [<ffffffff811b9538>] SyS_ioctl+0x88/0xa0
> [<ffffffff8152a5c9>] system_call_fastpath+0x16/0x1b
>
> The problem is caused by recover_bitmaps can't reliably abort
> when the thread is unregistered. So dlm_lock_sync_interruptible
> is introduced to detect the thread's situation to fix the problem.
>
> Reviewed-by: NeilBrown <neilb@xxxxxxxx>
> Signed-off-by: Guoqing Jiang <gqjiang@xxxxxxxx>
> ---
> drivers/md/md-cluster.c | 38 +++++++++++++++++++++++++++++++++++++-
> 1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
> index ea2699e..f3d584e 100644
> --- a/drivers/md/md-cluster.c
> +++ b/drivers/md/md-cluster.c
> @@ -10,6 +10,8 @@
>
>
> #include <linux/module.h>
> +#include <linux/completion.h>
> +#include <linux/kthread.h>
> #include <linux/dlm.h>
> #include <linux/sched.h>
> #include <linux/raid/md_p.h>
> @@ -141,6 +143,40 @@ static int dlm_unlock_sync(struct dlm_lock_resource *res)
> return dlm_lock_sync(res, DLM_LOCK_NL);
> }
>
> +/* An variation of dlm_lock_sync, which make lock request could
> + * be interrupted */
> +static int dlm_lock_sync_interruptible(struct dlm_lock_resource *res, int mode,
> + struct mddev *mddev)
> +{
> + int ret = 0;
> +
> + ret = dlm_lock(res->ls, mode, &res->lksb,
> + res->flags, res->name, strlen(res->name),
> + 0, sync_ast, res, res->bast);
> + if (ret)
> + return ret;
> +
> + wait_event(res->completion.wait,
> + res->completion.done || kthread_should_stop());
can you convert it to a waitq? Directly using the .wait/.done of completion is
really intrusive.
> + if (!res->completion.done) {
> + /*
> + * the convert queue contains the lock request when request is
> + * interrupted, and sync_ast could still be run, so need to
> + * cancel the request and reset completion
> + */
> + ret = dlm_unlock(res->ls, res->lksb.sb_lkid, DLM_LKF_CANCEL, &res->lksb, res);
> + reinit_completion(&res->completion);
> + if (unlikely(ret != 0))
> + pr_info("failed to cancel previous lock request "
> + "%s return %d\n", res->name, ret);
> + return -EPERM;
> + }
> + wait_for_completion(&res->completion);
> + if (res->lksb.sb_status == 0)
> + res->mode = mode;
> + return res->lksb.sb_status;
> +}
> +
> static struct dlm_lock_resource *lockres_init(struct mddev *mddev,
> char *name, void (*bastfn)(void *arg, int mode), int with_lvb)
> {
> @@ -272,7 +308,7 @@ static void recover_bitmaps(struct md_thread *thread)
> goto clear_bit;
> }
>
> - ret = dlm_lock_sync(bm_lockres, DLM_LOCK_PW);
> + ret = dlm_lock_sync_interruptible(bm_lockres, DLM_LOCK_PW, mddev);
> if (ret) {
> pr_err("md-cluster: Could not DLM lock %s: %d\n",
> str, ret);
> --
> 2.6.2
>
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