Re: [EXTERNAL] [PATCH v2 6/7] ceph: add manual reset debugfs control and tracepoints

[Viacheslav Dubeyko]

On Wed, 2026-04-15 at 17:00 +0000, Alex Markuze wrote:
> Add the debugfs and trace plumbing used to trigger and observe
> manual client reset.
> 
> The reset interface exposes a trigger file for operator-initiated
> reset and a status file for tracking the most recent run.  The
> tracepoints record scheduling, completion, and blocked caller
> behavior so reset progress can be diagnosed from the client side.
> 
> debugfs layout under /sys/kernel/debug/ceph/<client>/reset/:
>   trigger - write to initiate a manual reset
>   status  - read to see the most recent reset result
> 
> Tracepoints:
>   ceph_client_reset_schedule  - reset queued
>   ceph_client_reset_complete  - reset finished (success or failure)
>   ceph_client_reset_blocked   - caller blocked waiting for reset
>   ceph_client_reset_unblocked - caller unblocked after reset
> 
> Signed-off-by: Alex Markuze <amarkuze@xxxxxxxxxx>
> ---
>  fs/ceph/debugfs.c           | 104 ++++++++++++++++++++++++++++++++++++
>  fs/ceph/mds_client.c        |   8 +++
>  fs/ceph/super.h             |   3 ++
>  include/trace/events/ceph.h |  63 ++++++++++++++++++++++
>  4 files changed, 178 insertions(+)
> 
> diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
> index 7dc307790240..d46d41ec7a86 100644
> --- a/fs/ceph/debugfs.c
> +++ b/fs/ceph/debugfs.c
> @@ -9,6 +9,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/math64.h>
>  #include <linux/ktime.h>
> +#include <linux/uaccess.h>
>  
>  #include <linux/ceph/libceph.h>
>  #include <linux/ceph/mon_client.h>
> @@ -360,16 +361,107 @@ static int status_show(struct seq_file *s, void *p)
>  	return 0;
>  }
>  
> +static int reset_status_show(struct seq_file *s, void *p)
> +{
> +	struct ceph_fs_client *fsc = s->private;
> +	struct ceph_mds_client *mdsc = fsc->mdsc;
> +	struct ceph_client_reset_state *st;
> +	u64 trigger = 0, success = 0, failure = 0;
> +	unsigned long last_start = 0, last_finish = 0;
> +	int last_errno = 0;
> +	enum ceph_client_reset_phase phase = CEPH_CLIENT_RESET_IDLE;
> +	bool drain_timed_out = false;
> +	int sessions_reset = 0;
> +	int blocked_requests = 0;
> +	char reason[CEPH_CLIENT_RESET_REASON_LEN];
> +
> +	if (!mdsc)
> +		return 0;
> +
> +	st = &mdsc->reset_state;
> +
> +	spin_lock(&st->lock);
> +	trigger = st->trigger_count;
> +	success = st->success_count;
> +	failure = st->failure_count;
> +	last_start = st->last_start;
> +	last_finish = st->last_finish;
> +	last_errno = st->last_errno;
> +	phase = st->phase;
> +	drain_timed_out = st->drain_timed_out;
> +	sessions_reset = st->sessions_reset;
> +	strscpy(reason, st->last_reason, sizeof(reason));
> +	spin_unlock(&st->lock);
> +
> +	blocked_requests = atomic_read(&st->blocked_requests);
> +
> +	seq_printf(s, "phase: %s\n", ceph_reset_phase_name(phase));
> +	seq_printf(s, "trigger_count: %llu\n", trigger);
> +	seq_printf(s, "success_count: %llu\n", success);
> +	seq_printf(s, "failure_count: %llu\n", failure);
> +	if (last_start)
> +		seq_printf(s, "last_start_ms_ago: %u\n",
> +			   jiffies_to_msecs(jiffies - last_start));
> +	else
> +		seq_puts(s, "last_start_ms_ago: (never)\n");
> +	if (last_finish)
> +		seq_printf(s, "last_finish_ms_ago: %u\n",
> +			   jiffies_to_msecs(jiffies - last_finish));
> +	else
> +		seq_puts(s, "last_finish_ms_ago: (never)\n");
> +	seq_printf(s, "last_errno: %d\n", last_errno);
> +	seq_printf(s, "last_reason: %s\n",
> +		   reason[0] ? reason : "(none)");
> +	seq_printf(s, "drain_timed_out: %s\n",
> +		   drain_timed_out ? "yes" : "no");
> +	seq_printf(s, "sessions_reset: %d\n", sessions_reset);
> +	seq_printf(s, "blocked_requests: %d\n", blocked_requests);
> +
> +	return 0;
> +}
> +
> +static ssize_t reset_trigger_write(struct file *file, const char __user *buf,
> +				   size_t len, loff_t *ppos)
> +{
> +	struct ceph_fs_client *fsc = file->private_data;
> +	struct ceph_mds_client *mdsc = fsc->mdsc;
> +	char reason[CEPH_CLIENT_RESET_REASON_LEN];
> +	size_t copy;
> +	int ret;
> +
> +	if (!mdsc)
> +		return -ENODEV;
> +
> +	copy = min_t(size_t, len, sizeof(reason) - 1);
> +	if (copy && copy_from_user(reason, buf, copy))
> +		return -EFAULT;
> +	reason[copy] = '\0';
> +	strim(reason);
> +
> +	ret = ceph_mdsc_schedule_reset(mdsc, reason);
> +	if (ret)
> +		return ret;
> +
> +	return len;
> +}
> +
>  DEFINE_SHOW_ATTRIBUTE(mdsmap);
>  DEFINE_SHOW_ATTRIBUTE(mdsc);
>  DEFINE_SHOW_ATTRIBUTE(caps);
>  DEFINE_SHOW_ATTRIBUTE(mds_sessions);
>  DEFINE_SHOW_ATTRIBUTE(status);
> +DEFINE_SHOW_ATTRIBUTE(reset_status);
>  DEFINE_SHOW_ATTRIBUTE(metrics_file);
>  DEFINE_SHOW_ATTRIBUTE(metrics_latency);
>  DEFINE_SHOW_ATTRIBUTE(metrics_size);
>  DEFINE_SHOW_ATTRIBUTE(metrics_caps);
>  
> +static const struct file_operations ceph_reset_trigger_fops = {
> +	.owner = THIS_MODULE,
> +	.open = simple_open,
> +	.write = reset_trigger_write,
> +	.llseek = noop_llseek,
> +};
>  
>  /*
>   * debugfs
> @@ -404,6 +496,7 @@ void ceph_fs_debugfs_cleanup(struct ceph_fs_client *fsc)
>  	debugfs_remove(fsc->debugfs_caps);
>  	debugfs_remove(fsc->debugfs_status);
>  	debugfs_remove(fsc->debugfs_mdsc);
> +	debugfs_remove_recursive(fsc->debugfs_reset_dir);
>  	debugfs_remove_recursive(fsc->debugfs_metrics_dir);
>  	doutc(fsc->client, "done\n");
>  }
> @@ -451,6 +544,17 @@ void ceph_fs_debugfs_init(struct ceph_fs_client *fsc)
>  						fsc,
>  						&caps_fops);
>  
> +	fsc->debugfs_reset_dir = debugfs_create_dir("reset",
> +						    fsc->client->debugfs_dir);
> +	fsc->debugfs_reset_trigger =
> +		debugfs_create_file("trigger", 0200,
> +				    fsc->debugfs_reset_dir, fsc,
> +				    &ceph_reset_trigger_fops);
> +	fsc->debugfs_reset_status =
> +		debugfs_create_file("status", 0400,
> +				    fsc->debugfs_reset_dir, fsc,
> +				    &reset_status_fops);
> +
>  	fsc->debugfs_status = debugfs_create_file("status",
>  						  0400,
>  						  fsc->client->debugfs_dir,
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 7e399b0dcc55..98a882cf8b65 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -5213,6 +5213,7 @@ int ceph_mdsc_wait_for_reset(struct ceph_mds_client *mdsc)
>  	blocked_count = atomic_inc_return(&st->blocked_requests);
>  	doutc(cl, "request blocked during reset, %d total blocked\n",
>  	      blocked_count);
> +	trace_ceph_client_reset_blocked(mdsc, blocked_count);
>  
>  retry:
>  	wait_ret = wait_event_interruptible_timeout(st->blocked_wq,
> @@ -5223,10 +5224,12 @@ int ceph_mdsc_wait_for_reset(struct ceph_mds_client *mdsc)
>  	if (wait_ret == 0) {
>  		atomic_dec(&st->blocked_requests);
>  		pr_warn_client(cl, "timed out waiting for reset to complete\n");
> +		trace_ceph_client_reset_unblocked(mdsc, -ETIMEDOUT);
>  		return -ETIMEDOUT;
>  	}
>  	if (wait_ret < 0) {
>  		atomic_dec(&st->blocked_requests);
> +		trace_ceph_client_reset_unblocked(mdsc, (int)wait_ret);
>  		return (int)wait_ret;  /* -ERESTARTSYS */
>  	}
>  
> @@ -5241,12 +5244,14 @@ int ceph_mdsc_wait_for_reset(struct ceph_mds_client *mdsc)
>  		if (time_before(jiffies, deadline))
>  			goto retry;
>  		atomic_dec(&st->blocked_requests);
> +		trace_ceph_client_reset_unblocked(mdsc, -ETIMEDOUT);
>  		return -ETIMEDOUT;
>  	}
>  	ret = st->last_errno;
>  	spin_unlock(&st->lock);
>  
>  	atomic_dec(&st->blocked_requests);
> +	trace_ceph_client_reset_unblocked(mdsc, ret);
>  	return ret;
>  }
>  
> @@ -5275,6 +5280,8 @@ static void ceph_mdsc_reset_complete(struct ceph_mds_client *mdsc, int ret)
>  
>  	/* Wake up all requests that were blocked waiting for reset */
>  	wake_up_all(&st->blocked_wq);
> +
> +	trace_ceph_client_reset_complete(mdsc, ret);
>  }
>  
>  static void ceph_mdsc_reset_workfn(struct work_struct *work)
> @@ -5559,6 +5566,7 @@ int ceph_mdsc_schedule_reset(struct ceph_mds_client *mdsc,
>  	pr_info_client(mdsc->fsc->client,
>  		       "manual session reset scheduled (reason=\"%s\")\n",
>  		       msg);
> +	trace_ceph_client_reset_schedule(mdsc, msg);
>  	return 0;
>  }
>  
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index 1f901b1647e6..98af0a823c81 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -179,6 +179,9 @@ struct ceph_fs_client {
>  	struct dentry *debugfs_status;
>  	struct dentry *debugfs_mds_sessions;
>  	struct dentry *debugfs_metrics_dir;
> +	struct dentry *debugfs_reset_dir;
> +	struct dentry *debugfs_reset_trigger;
> +	struct dentry *debugfs_reset_status;

The debugfs_reset_trigger and debugfs_reset_status initialized in
ceph_fs_debugfs_init() but never used in any methods. Do we really need these
fields?

>  #endif
>  
>  #ifdef CONFIG_CEPH_FSCACHE
> diff --git a/include/trace/events/ceph.h b/include/trace/events/ceph.h
> index 08cb0659fbfc..e853c891ef71 100644
> --- a/include/trace/events/ceph.h
> +++ b/include/trace/events/ceph.h
> @@ -226,6 +226,69 @@ TRACE_EVENT(ceph_handle_caps,
>  		  __entry->mseq)
>  );
>  
> +/*
> + * Client reset tracepoints - identify the client by its monitor-
> + * assigned global_id so traces remain meaningful when kernel pointer
> + * hashing is enabled.
> + */
> +TRACE_EVENT(ceph_client_reset_schedule,
> +	TP_PROTO(const struct ceph_mds_client *mdsc, const char *reason),
> +	TP_ARGS(mdsc, reason),
> +	TP_STRUCT__entry(
> +		__field(u64, client_id)
> +		__string(reason, reason ? reason : "")
> +	),
> +	TP_fast_assign(
> +		__entry->client_id = mdsc->fsc->client->monc.auth->global_id;

All four tracepoints dereference mdsc->fsc->client->monc.auth->global_id. Could
monc.auth be NULL during early client init or late teardown?

Thanks,
Slava.

> +		__assign_str(reason);
> +	),
> +	TP_printk("client_id=%llu reason=%s",
> +		  __entry->client_id, __get_str(reason))
> +);
> +
> +TRACE_EVENT(ceph_client_reset_complete,
> +	TP_PROTO(const struct ceph_mds_client *mdsc, int ret),
> +	TP_ARGS(mdsc, ret),
> +	TP_STRUCT__entry(
> +		__field(u64, client_id)
> +		__field(int, ret)
> +	),
> +	TP_fast_assign(
> +		__entry->client_id = mdsc->fsc->client->monc.auth->global_id;
> +		__entry->ret = ret;
> +	),
> +	TP_printk("client_id=%llu ret=%d", __entry->client_id, __entry->ret)
> +);
> +
> +TRACE_EVENT(ceph_client_reset_blocked,
> +	TP_PROTO(const struct ceph_mds_client *mdsc, int blocked_count),
> +	TP_ARGS(mdsc, blocked_count),
> +	TP_STRUCT__entry(
> +		__field(u64, client_id)
> +		__field(int, blocked_count)
> +	),
> +	TP_fast_assign(
> +		__entry->client_id = mdsc->fsc->client->monc.auth->global_id;
> +		__entry->blocked_count = blocked_count;
> +	),
> +	TP_printk("client_id=%llu blocked_count=%d", __entry->client_id,
> +		  __entry->blocked_count)
> +);
> +
> +TRACE_EVENT(ceph_client_reset_unblocked,
> +	TP_PROTO(const struct ceph_mds_client *mdsc, int ret),
> +	TP_ARGS(mdsc, ret),
> +	TP_STRUCT__entry(
> +		__field(u64, client_id)
> +		__field(int, ret)
> +	),
> +	TP_fast_assign(
> +		__entry->client_id = mdsc->fsc->client->monc.auth->global_id;
> +		__entry->ret = ret;
> +	),
> +	TP_printk("client_id=%llu ret=%d", __entry->client_id, __entry->ret)
> +);
> +
>  #undef EM
>  #undef E_
>  #endif /* _TRACE_CEPH_H */