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SubjectRe: [PATCH v2] ocfs2: ocfs2_downconvert_lock failure results in deadlock
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On 8/30/21 12:46 PM, Gang He wrote:
> Usually, ocfs2_downconvert_lock() function always downconverts
> dlm lock to the expected level for satisfy dlm bast requests
> from the other nodes.
> But there is a rare situation. When dlm lock conversion is being
> canceled, ocfs2_downconvert_lock() function will return -EBUSY.
> You need to be aware that ocfs2_cancel_convert() function is
> asynchronous in fsdlm implementation.
> If we does not requeue this lockres entry, ocfs2 downconvert
> thread no longer handles this dlm lock bast request. Then, the
> other nodes will not get the dlm lock again, the current node's
> process will be blocked when acquire this dlm lock again.
>
> Signed-off-by: Gang He <ghe@suse.com>

Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> ---
> v2: keep error print in ocfs2_downconvert_lock function, add more detailed
> comments in code, add msleep to avoid repeated attempts.
> ---
> fs/ocfs2/dlmglue.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 48fd369c29a4..f8f561850470 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -16,6 +16,7 @@
> #include <linux/debugfs.h>
> #include <linux/seq_file.h>
> #include <linux/time.h>
> +#include <linux/delay.h>
> #include <linux/quotaops.h>
> #include <linux/sched/signal.h>
>
> @@ -3912,6 +3913,17 @@ static int ocfs2_unblock_lock(struct ocfs2_super *osb,
> spin_unlock_irqrestore(&lockres->l_lock, flags);
> ret = ocfs2_downconvert_lock(osb, lockres, new_level, set_lvb,
> gen);
> + /* The dlm lock convert is being cancelled in background,
> + * ocfs2_cancel_convert() is asynchronous in fs/dlm,
> + * requeue it, try again later.
> + */
> + if (ret == -EBUSY) {
> + ctl->requeue = 1;
> + mlog(ML_BASTS, "lockres %s, ReQ: Downconvert busy\n",
> + lockres->l_name);
> + ret = 0;
> + msleep(20);
> + }
>
> leave:
> if (ret)
>

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