[PATCH RFC 0/2] Reduce size of stack frame in svc_export_parse()

[PATCH RFC 0/2] Reduce size of stack frame in svc_export_parse()

[Chuck Lever]

Here's a possible way to address a recent 0-day report.
Compile-tested only.

---

Chuck Lever (2):
      NFSD: Rewrite synopsis of nfsd_percpu_counters_init()
      NFSD: Fix frame size warning in svc_export_parse()


 fs/nfsd/export.c | 30 +++++++++++++++++++++---------
 fs/nfsd/export.h |  4 ++--
 fs/nfsd/stats.c  |  2 +-
 fs/nfsd/stats.h  | 18 +++++++++---------
 4 files changed, 33 insertions(+), 21 deletions(-)

--
Chuck Lever

[PATCH RFC 1/2] NFSD: Rewrite synopsis of nfsd_percpu_counters_init()

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

In function ‘export_stats_init’,
    inlined from ‘svc_export_alloc’ at /home/cel/src/linux/server-development/fs/nfsd/export.c:866:6:
/home/cel/src/linux/server-development/fs/nfsd/export.c:337:16: warning: ‘nfsd_percpu_counters_init’ accessing 40 bytes in a region of size 0 [-Wstringop-overflow=]
  337 |         return nfsd_percpu_counters_init(&stats->counter, EXP_STATS_COUNTERS_NUM);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/cel/src/linux/server-development/fs/nfsd/export.c:337:16: note: referencing argument 1 of type ‘struct percpu_counter[0]’
/home/cel/src/linux/server-development/fs/nfsd/stats.h: In function ‘svc_export_alloc’:
/home/cel/src/linux/server-development/fs/nfsd/stats.h:40:5: note: in a call to function ‘nfsd_percpu_counters_init’
   40 | int nfsd_percpu_counters_init(struct percpu_counter counters[], int num);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/stats.c |    2 +-
 fs/nfsd/stats.h |    6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
index 63797635e1c3..12c299a05433 100644
--- a/fs/nfsd/stats.c
+++ b/fs/nfsd/stats.c
@@ -76,7 +76,7 @@ static int nfsd_show(struct seq_file *seq, void *v)
 
 DEFINE_PROC_SHOW_ATTRIBUTE(nfsd);
 
-int nfsd_percpu_counters_init(struct percpu_counter counters[], int num)
+int nfsd_percpu_counters_init(struct percpu_counter *counters, int num)
 {
 	int i, err = 0;
 
diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
index cf5524e7ca06..a3e9e2f47ec4 100644
--- a/fs/nfsd/stats.h
+++ b/fs/nfsd/stats.h
@@ -37,9 +37,9 @@ extern struct nfsd_stats	nfsdstats;
 
 extern struct svc_stat		nfsd_svcstats;
 
-int nfsd_percpu_counters_init(struct percpu_counter counters[], int num);
-void nfsd_percpu_counters_reset(struct percpu_counter counters[], int num);
-void nfsd_percpu_counters_destroy(struct percpu_counter counters[], int num);
+int nfsd_percpu_counters_init(struct percpu_counter *counters, int num);
+void nfsd_percpu_counters_reset(struct percpu_counter *counters, int num);
+void nfsd_percpu_counters_destroy(struct percpu_counter *counters, int num);
 int nfsd_stat_init(void);
 void nfsd_stat_shutdown(void);
 

[PATCH RFC 2/2] NFSD: Fix frame size warning in svc_export_parse()

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/export.c: In function 'svc_export_parse':
fs/nfsd/export.c:737:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
    737 | }

On my systems, svc_export_parse() has a stack frame of over 800
bytes, not 1040, but nonetheless, it could do with some reduction.

When a struct svc_export is on the stack, it's a temporary structure
used as an argument, and not visible as an actual exported FS. No
need to reserve space for export_stats in such cases.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310012359.YEw5IrK6-lkp@intel.com/
Cc: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/export.c |   30 +++++++++++++++++++++---------
 fs/nfsd/export.h |    4 ++--
 fs/nfsd/stats.h  |   12 ++++++------
 3 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 11a0eaa2f914..7cf26bfe199d 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -339,12 +339,16 @@ static int export_stats_init(struct export_stats *stats)
 
 static void export_stats_reset(struct export_stats *stats)
 {
-	nfsd_percpu_counters_reset(stats->counter, EXP_STATS_COUNTERS_NUM);
+	if (stats)
+		nfsd_percpu_counters_reset(stats->counter,
+					   EXP_STATS_COUNTERS_NUM);
 }
 
 static void export_stats_destroy(struct export_stats *stats)
 {
-	nfsd_percpu_counters_destroy(stats->counter, EXP_STATS_COUNTERS_NUM);
+	if (stats)
+		nfsd_percpu_counters_destroy(stats->counter,
+					     EXP_STATS_COUNTERS_NUM);
 }
 
 static void svc_export_put(struct kref *ref)
@@ -353,7 +357,8 @@ static void svc_export_put(struct kref *ref)
 	path_put(&exp->ex_path);
 	auth_domain_put(exp->ex_client);
 	nfsd4_fslocs_free(&exp->ex_fslocs);
-	export_stats_destroy(&exp->ex_stats);
+	export_stats_destroy(exp->ex_stats);
+	kfree(exp->ex_stats);
 	kfree(exp->ex_uuid);
 	kfree_rcu(exp, ex_rcu);
 }
@@ -767,13 +772,13 @@ static int svc_export_show(struct seq_file *m,
 	seq_putc(m, '\t');
 	seq_escape(m, exp->ex_client->name, " \t\n\\");
 	if (export_stats) {
-		seq_printf(m, "\t%lld\n", exp->ex_stats.start_time);
+		seq_printf(m, "\t%lld\n", exp->ex_stats->start_time);
 		seq_printf(m, "\tfh_stale: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_FH_STALE]));
+			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_FH_STALE]));
 		seq_printf(m, "\tio_read: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_READ]));
+			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_IO_READ]));
 		seq_printf(m, "\tio_write: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_WRITE]));
+			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_IO_WRITE]));
 		seq_putc(m, '\n');
 		return 0;
 	}
@@ -819,7 +824,7 @@ static void svc_export_init(struct cache_head *cnew, struct cache_head *citem)
 	new->ex_layout_types = 0;
 	new->ex_uuid = NULL;
 	new->cd = item->cd;
-	export_stats_reset(&new->ex_stats);
+	export_stats_reset(new->ex_stats);
 }
 
 static void export_update(struct cache_head *cnew, struct cache_head *citem)
@@ -856,7 +861,14 @@ static struct cache_head *svc_export_alloc(void)
 	if (!i)
 		return NULL;
 
-	if (export_stats_init(&i->ex_stats)) {
+	i->ex_stats = kmalloc(sizeof(i->ex_stats), GFP_KERNEL);
+	if (!i->ex_stats) {
+		kfree(i);
+		return NULL;
+	}
+
+	if (export_stats_init(i->ex_stats)) {
+		kfree(i->ex_stats);
 		kfree(i);
 		return NULL;
 	}
diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
index 2df8ae25aad3..ca9dc230ae3d 100644
--- a/fs/nfsd/export.h
+++ b/fs/nfsd/export.h
@@ -64,10 +64,10 @@ struct svc_export {
 	struct cache_head	h;
 	struct auth_domain *	ex_client;
 	int			ex_flags;
+	int			ex_fsid;
 	struct path		ex_path;
 	kuid_t			ex_anon_uid;
 	kgid_t			ex_anon_gid;
-	int			ex_fsid;
 	unsigned char *		ex_uuid; /* 16 byte fsid */
 	struct nfsd4_fs_locations ex_fslocs;
 	uint32_t		ex_nflavors;
@@ -76,8 +76,8 @@ struct svc_export {
 	struct nfsd4_deviceid_map *ex_devid_map;
 	struct cache_detail	*cd;
 	struct rcu_head		ex_rcu;
-	struct export_stats	ex_stats;
 	unsigned long		ex_xprtsec_modes;
+	struct export_stats	*ex_stats;
 };
 
 /* an "export key" (expkey) maps a filehandlefragement to an
diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
index a3e9e2f47ec4..14f50c660b61 100644
--- a/fs/nfsd/stats.h
+++ b/fs/nfsd/stats.h
@@ -61,22 +61,22 @@ static inline void nfsd_stats_rc_nocache_inc(void)
 static inline void nfsd_stats_fh_stale_inc(struct svc_export *exp)
 {
 	percpu_counter_inc(&nfsdstats.counter[NFSD_STATS_FH_STALE]);
-	if (exp)
-		percpu_counter_inc(&exp->ex_stats.counter[EXP_STATS_FH_STALE]);
+	if (exp && exp->ex_stats)
+		percpu_counter_inc(&exp->ex_stats->counter[EXP_STATS_FH_STALE]);
 }
 
 static inline void nfsd_stats_io_read_add(struct svc_export *exp, s64 amount)
 {
 	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_READ], amount);
-	if (exp)
-		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_READ], amount);
+	if (exp && exp->ex_stats)
+		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_READ], amount);
 }
 
 static inline void nfsd_stats_io_write_add(struct svc_export *exp, s64 amount)
 {
 	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_WRITE], amount);
-	if (exp)
-		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_WRITE], amount);
+	if (exp && exp->ex_stats)
+		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_WRITE], amount);
 }
 
 static inline void nfsd_stats_payload_misses_inc(struct nfsd_net *nn)

Re: [PATCH RFC 1/2] NFSD: Rewrite synopsis of nfsd_percpu_counters_init()

[Jeff Layton]

On Sun, 2023-10-01 at 13:25 -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> In function ‘export_stats_init’,
>     inlined from ‘svc_export_alloc’ at /home/cel/src/linux/server-development/fs/nfsd/export.c:866:6:
> /home/cel/src/linux/server-development/fs/nfsd/export.c:337:16: warning: ‘nfsd_percpu_counters_init’ accessing 40 bytes in a region of size 0 [-Wstringop-overflow=]
>   337 |         return nfsd_percpu_counters_init(&stats->counter, EXP_STATS_COUNTERS_NUM);
>       |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /home/cel/src/linux/server-development/fs/nfsd/export.c:337:16: note: referencing argument 1 of type ‘struct percpu_counter[0]’
> /home/cel/src/linux/server-development/fs/nfsd/stats.h: In function ‘svc_export_alloc’:
> /home/cel/src/linux/server-development/fs/nfsd/stats.h:40:5: note: in a call to function ‘nfsd_percpu_counters_init’
>    40 | int nfsd_percpu_counters_init(struct percpu_counter counters[], int num);
>       |     ^~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Cc: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/stats.c |    2 +-
>  fs/nfsd/stats.h |    6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
> index 63797635e1c3..12c299a05433 100644
> --- a/fs/nfsd/stats.c
> +++ b/fs/nfsd/stats.c
> @@ -76,7 +76,7 @@ static int nfsd_show(struct seq_file *seq, void *v)
>  
>  DEFINE_PROC_SHOW_ATTRIBUTE(nfsd);
>  
> -int nfsd_percpu_counters_init(struct percpu_counter counters[], int num)
> +int nfsd_percpu_counters_init(struct percpu_counter *counters, int num)
>  {
>  	int i, err = 0;
>  
> diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
> index cf5524e7ca06..a3e9e2f47ec4 100644
> --- a/fs/nfsd/stats.h
> +++ b/fs/nfsd/stats.h
> @@ -37,9 +37,9 @@ extern struct nfsd_stats	nfsdstats;
>  
>  extern struct svc_stat		nfsd_svcstats;
>  
> -int nfsd_percpu_counters_init(struct percpu_counter counters[], int num);
> -void nfsd_percpu_counters_reset(struct percpu_counter counters[], int num);
> -void nfsd_percpu_counters_destroy(struct percpu_counter counters[], int num);
> +int nfsd_percpu_counters_init(struct percpu_counter *counters, int num);
> +void nfsd_percpu_counters_reset(struct percpu_counter *counters, int num);
> +void nfsd_percpu_counters_destroy(struct percpu_counter *counters, int num);
>  int nfsd_stat_init(void);
>  void nfsd_stat_shutdown(void);
>  
> 
> 

Reviewed-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH RFC 2/2] NFSD: Fix frame size warning in svc_export_parse()

[Jeff Layton]

On Sun, 2023-10-01 at 13:25 -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> fs/nfsd/export.c: In function 'svc_export_parse':
> fs/nfsd/export.c:737:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>     737 | }
> 
> On my systems, svc_export_parse() has a stack frame of over 800
> bytes, not 1040, but nonetheless, it could do with some reduction.
> 
> When a struct svc_export is on the stack, it's a temporary structure
> used as an argument, and not visible as an actual exported FS. No
> need to reserve space for export_stats in such cases.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310012359.YEw5IrK6-lkp@intel.com/
> Cc: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/export.c |   30 +++++++++++++++++++++---------
>  fs/nfsd/export.h |    4 ++--
>  fs/nfsd/stats.h  |   12 ++++++------
>  3 files changed, 29 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index 11a0eaa2f914..7cf26bfe199d 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -339,12 +339,16 @@ static int export_stats_init(struct export_stats *stats)
>  
>  static void export_stats_reset(struct export_stats *stats)
>  {
> -	nfsd_percpu_counters_reset(stats->counter, EXP_STATS_COUNTERS_NUM);
> +	if (stats)
> +		nfsd_percpu_counters_reset(stats->counter,
> +					   EXP_STATS_COUNTERS_NUM);
>  }
>  
>  static void export_stats_destroy(struct export_stats *stats)
>  {
> -	nfsd_percpu_counters_destroy(stats->counter, EXP_STATS_COUNTERS_NUM);
> +	if (stats)
> +		nfsd_percpu_counters_destroy(stats->counter,
> +					     EXP_STATS_COUNTERS_NUM);
>  }
>  
>  static void svc_export_put(struct kref *ref)
> @@ -353,7 +357,8 @@ static void svc_export_put(struct kref *ref)
>  	path_put(&exp->ex_path);
>  	auth_domain_put(exp->ex_client);
>  	nfsd4_fslocs_free(&exp->ex_fslocs);
> -	export_stats_destroy(&exp->ex_stats);
> +	export_stats_destroy(exp->ex_stats);
> +	kfree(exp->ex_stats);
>  	kfree(exp->ex_uuid);
>  	kfree_rcu(exp, ex_rcu);
>  }
> @@ -767,13 +772,13 @@ static int svc_export_show(struct seq_file *m,
>  	seq_putc(m, '\t');
>  	seq_escape(m, exp->ex_client->name, " \t\n\\");
>  	if (export_stats) {
> -		seq_printf(m, "\t%lld\n", exp->ex_stats.start_time);
> +		seq_printf(m, "\t%lld\n", exp->ex_stats->start_time);
>  		seq_printf(m, "\tfh_stale: %lld\n",
> -			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_FH_STALE]));
> +			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_FH_STALE]));
>  		seq_printf(m, "\tio_read: %lld\n",
> -			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_READ]));
> +			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_IO_READ]));
>  		seq_printf(m, "\tio_write: %lld\n",
> -			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_WRITE]));
> +			   percpu_counter_sum_positive(&exp->ex_stats->counter[EXP_STATS_IO_WRITE]));
>  		seq_putc(m, '\n');
>  		return 0;
>  	}
> @@ -819,7 +824,7 @@ static void svc_export_init(struct cache_head *cnew, struct cache_head *citem)
>  	new->ex_layout_types = 0;
>  	new->ex_uuid = NULL;
>  	new->cd = item->cd;
> -	export_stats_reset(&new->ex_stats);
> +	export_stats_reset(new->ex_stats);
>  }
>  
>  static void export_update(struct cache_head *cnew, struct cache_head *citem)
> @@ -856,7 +861,14 @@ static struct cache_head *svc_export_alloc(void)
>  	if (!i)
>  		return NULL;
>  
> -	if (export_stats_init(&i->ex_stats)) {
> +	i->ex_stats = kmalloc(sizeof(i->ex_stats), GFP_KERNEL);
> +	if (!i->ex_stats) {
> +		kfree(i);
> +		return NULL;
> +	}
> +
> +	if (export_stats_init(i->ex_stats)) {
> +		kfree(i->ex_stats);
>  		kfree(i);
>  		return NULL;
>  	}
> diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
> index 2df8ae25aad3..ca9dc230ae3d 100644
> --- a/fs/nfsd/export.h
> +++ b/fs/nfsd/export.h
> @@ -64,10 +64,10 @@ struct svc_export {
>  	struct cache_head	h;
>  	struct auth_domain *	ex_client;
>  	int			ex_flags;
> +	int			ex_fsid;
>  	struct path		ex_path;
>  	kuid_t			ex_anon_uid;
>  	kgid_t			ex_anon_gid;
> -	int			ex_fsid;
>  	unsigned char *		ex_uuid; /* 16 byte fsid */
>  	struct nfsd4_fs_locations ex_fslocs;
>  	uint32_t		ex_nflavors;
> @@ -76,8 +76,8 @@ struct svc_export {
>  	struct nfsd4_deviceid_map *ex_devid_map;
>  	struct cache_detail	*cd;
>  	struct rcu_head		ex_rcu;
> -	struct export_stats	ex_stats;
>  	unsigned long		ex_xprtsec_modes;
> +	struct export_stats	*ex_stats;
>  };
>  
>  /* an "export key" (expkey) maps a filehandlefragement to an
> diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
> index a3e9e2f47ec4..14f50c660b61 100644
> --- a/fs/nfsd/stats.h
> +++ b/fs/nfsd/stats.h
> @@ -61,22 +61,22 @@ static inline void nfsd_stats_rc_nocache_inc(void)
>  static inline void nfsd_stats_fh_stale_inc(struct svc_export *exp)
>  {
>  	percpu_counter_inc(&nfsdstats.counter[NFSD_STATS_FH_STALE]);
> -	if (exp)
> -		percpu_counter_inc(&exp->ex_stats.counter[EXP_STATS_FH_STALE]);
> +	if (exp && exp->ex_stats)
> +		percpu_counter_inc(&exp->ex_stats->counter[EXP_STATS_FH_STALE]);
>  }
>  
>  static inline void nfsd_stats_io_read_add(struct svc_export *exp, s64 amount)
>  {
>  	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_READ], amount);
> -	if (exp)
> -		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_READ], amount);
> +	if (exp && exp->ex_stats)
> +		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_READ], amount);
>  }
>  
>  static inline void nfsd_stats_io_write_add(struct svc_export *exp, s64 amount)
>  {
>  	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_WRITE], amount);
> -	if (exp)
> -		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_WRITE], amount);
> +	if (exp && exp->ex_stats)
> +		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_WRITE], amount);
>  }
>  
>  static inline void nfsd_stats_payload_misses_inc(struct nfsd_net *nn)
> 
> 

Seems reasonable.

Reviewed-by: Jeff Layton <jlayton@kernel.org>