diff mbox series

[v2,1/2] net: extend drop reasons for multiple subsystems

Message ID 20230330212227.928595-1-johannes@sipsolutions.net (mailing list archive)
State Changes Requested
Delegated to: Netdev Maintainers
Headers show
Series [v2,1/2] net: extend drop reasons for multiple subsystems | expand

Checks

Context Check Description
netdev/series_format warning Single patches do not need cover letters; Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit fail Errors and warnings before: 5281 this patch: 5282
netdev/cc_maintainers fail 5 maintainers not CCed: nhorman@tuxdriver.com pabeni@redhat.com kuba@kernel.org edumazet@google.com davem@davemloft.net
netdev/build_clang success Errors and warnings before: 1026 this patch: 1026
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn fail Errors and warnings before: 5489 this patch: 5490
netdev/checkpatch fail ERROR: code indent should use tabs where possible WARNING: line length of 92 exceeds 80 columns
netdev/kdoc fail Errors and warnings before: 1 this patch: 2
netdev/source_inline success Was 0 now: 0

Commit Message

Johannes Berg March 30, 2023, 9:22 p.m. UTC 
From: Johannes Berg <johannes.berg@intel.com>

Extend drop reasons to make them usable by subsystems
other than core by reserving the high 16 bits for a
new subsystem ID, of which 0 of course is used for the
existing reasons immediately.

To still be able to have string reasons, restructure
that code a bit to make the loopup under RCU, the only
user of this (right now) is drop_monitor.

Link: https://lore.kernel.org/netdev/00659771ed54353f92027702c5bbb84702da62ce.camel@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/dropreason.h | 37 ++++++++++++++++++++++---
 net/core/drop_monitor.c  | 32 +++++++++++++++-------
 net/core/skbuff.c        | 58 +++++++++++++++++++++++++++++++++++++---
 3 files changed, 111 insertions(+), 16 deletions(-)

Comments

Jakub Kicinski April 1, 2023, 4:36 a.m. UTC | #1 
On Thu, 30 Mar 2023 23:22:26 +0200 Johannes Berg wrote:
> diff --git a/include/net/dropreason.h b/include/net/dropreason.h
> index c0a3ea806cd5..d7a134c108ad 100644
> --- a/include/net/dropreason.h
> +++ b/include/net/dropreason.h
> @@ -339,10 +339,28 @@ enum skb_drop_reason {
>  	 */
>  	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
>  	/**
> -	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
> -	 * used as a real 'reason'
> -	 */
> +	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
> +	 * shouldn't be used as a real 'reason' - only for tracing code gen
> +         */
>  	SKB_DROP_REASON_MAX,
> +
> +	/** @SKB_DROP_REASON_SUBSYS_MASK: subsystem mask in drop reasons,
> +	 * see &enum skb_drop_reason_subsys
> +	 */
> +	SKB_DROP_REASON_SUBSYS_MASK = 0xffff0000,
> +};
> +
> +#define SKB_DROP_REASON_SUBSYS_SHIFT	16
> +
> +/**
> + * enum skb_drop_reason_subsys - subsystem tag for (extended) drop reasons
> + */
> +enum skb_drop_reason_subsys {
> +	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
> +	SKB_DROP_REASON_SUBSYS_CORE,
> +
> +	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
> +	SKB_DROP_REASON_SUBSYS_NUM
>  };
>  
>  #define SKB_DR_INIT(name, reason)				\
> @@ -358,6 +376,17 @@ enum skb_drop_reason {
>  			SKB_DR_SET(name, reason);		\
>  	} while (0)
>  
> -extern const char * const drop_reasons[];
> +struct drop_reason_list {
> +	const char * const *reasons;
> +	size_t n_reasons;
> +};
> +
> +/* Note: due to dynamic registrations, access must be under RCU */
> +extern const struct drop_reason_list __rcu *
> +drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
> +
> +void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
> +				  const struct drop_reason_list *list);
> +void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);

dropreason.h is included by skbuff.h because history, but I don't think
any of the new stuff must be visible in skbuff.h.

Could you make a new header, and put as much of this stuff there as
possible? Our future selves will thank us for shorter rebuild times..

>  #undef FN
>  #define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
> -const char * const drop_reasons[] = {
> +static const char * const drop_reasons[] = {
>  	[SKB_CONSUMED] = "CONSUMED",
>  	DEFINE_DROP_REASON(FN, FN)
>  };
> -EXPORT_SYMBOL(drop_reasons);
> +
> +static const struct drop_reason_list drop_reasons_core = {
> +	.reasons = drop_reasons,
> +	.n_reasons = ARRAY_SIZE(drop_reasons),
> +};
> +
> +const struct drop_reason_list __rcu *
> +drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
> +	[SKB_DROP_REASON_SUBSYS_CORE] = &drop_reasons_core,
> +};
> +EXPORT_SYMBOL(drop_reasons_by_subsys);
> +
> +/**
> + * drop_reasons_register_subsys - register another drop reason subsystem
> + * @subsys: the subsystem to register, must not be the core
> + * @list: the list of drop reasons within the subsystem, must point to
> + *	a statically initialized list
> + */
> +void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
> +				  const struct drop_reason_list *list)
> +{
> +	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
> +		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
> +		 "invalid subsystem %d\n", subsys))
> +		return;
> +
> +	/* must point to statically allocated memory, so INIT is OK */
> +	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], list);
> +}
> +EXPORT_SYMBOL_GPL(drop_reasons_register_subsys);
> +
> +/**
> + * drop_reasons_unregister_subsys - unregister a drop reason subsystem
> + * @subsys: the subsystem to remove, must not be the core
> + *
> + * Note: This will synchronize_rcu() to ensure no users when it returns.
> + */
> +void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys)
> +{
> +	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
> +		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
> +		 "invalid subsystem %d\n", subsys))
> +		return;
> +
> +	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], NULL);
> +
> +	synchronize_rcu();
> +}
> +EXPORT_SYMBOL_GPL(drop_reasons_unregister_subsys);

Weak preference to also take the code out of skbuff.c but that's not as
important.


You To'd both wireless and netdev, who are you expecting to apply this?
:S
kernel test robot April 14, 2023, 3:21 a.m. UTC | #2 
Hi Johannes,

kernel test robot noticed the following build warnings:

[auto build test WARNING on wireless-next/main]
[also build test WARNING on wireless/main horms-ipvs/master net/main net-next/main linus/master v6.3-rc6 next-20230413]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Johannes-Berg/mac80211-use-the-new-drop-reasons-infrastructure/20230331-052445
base:   https://git.kernel.org/pub/scm/linux/kernel/git/wireless/wireless-next.git main
patch link:    https://lore.kernel.org/r/20230330212227.928595-1-johannes%40sipsolutions.net
patch subject: [PATCH v2 1/2] net: extend drop reasons for multiple subsystems
config: m68k-randconfig-s042-20230413 (https://download.01.org/0day-ci/archive/20230414/202304141104.ixaAlfxh-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-39-gce1a6720-dirty
        # https://github.com/intel-lab-lkp/linux/commit/64925179be74db98280d706236e37e05bf7b5cca
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Johannes-Berg/mac80211-use-the-new-drop-reasons-infrastructure/20230331-052445
        git checkout 64925179be74db98280d706236e37e05bf7b5cca
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=m68k olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=m68k SHELL=/bin/bash net/core/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304141104.ixaAlfxh-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> net/core/skbuff.c:138:42: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct drop_reason_list const [noderef] __rcu * @@     got struct drop_reason_list const * @@
   net/core/skbuff.c:138:42: sparse:     expected struct drop_reason_list const [noderef] __rcu *
   net/core/skbuff.c:138:42: sparse:     got struct drop_reason_list const *

vim +138 net/core/skbuff.c

   135	
   136	const struct drop_reason_list __rcu *
   137	drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
 > 138		[SKB_DROP_REASON_SUBSYS_CORE] = &drop_reasons_core,
   139	};
   140	EXPORT_SYMBOL(drop_reasons_by_subsys);
   141
Johannes Berg April 14, 2023, 9:25 a.m. UTC | #3 
On Fri, 2023-03-31 at 21:36 -0700, Jakub Kicinski wrote:
> 
> > +/* Note: due to dynamic registrations, access must be under RCU */
> > +extern const struct drop_reason_list __rcu *
> > +drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
> > +
> > +void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
> > +				  const struct drop_reason_list *list);
> > +void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
> 
> dropreason.h is included by skbuff.h because history, but I don't think
> any of the new stuff must be visible in skbuff.h.
> 
> Could you make a new header, and put as much of this stuff there as
> possible? Our future selves will thank us for shorter rebuild times..

Sure. Not sure it'll make a big difference in rebuild, but we'll see :)

I ended up moving dropreason.h to dropreason-core.h first, that way we
also have a naming scheme for non-core dropreason files should they
become visible outside of the subsystem (i.e. mac80211 just has them
internally).

Dunno, let me know if you prefer something else, I just couldn't come up
with a non-confusing longer name for the new thing.

> Weak preference to also take the code out of skbuff.c but that's not as
> important.

I guess I can create a new dropreason.c, but is that worth it? It's only
a few lines. Let me know, then I can resend.

> You To'd both wireless and netdev, who are you expecting to apply this?
> :S

Good question :)

The first patch (patches in v3) really should go through net-next I
suppose, and I wouldn't mind if the other one did as well, it doesn't
right now touch anything likely to change.

johannes
Jakub Kicinski April 14, 2023, 2:42 p.m. UTC | #4 
On Fri, 14 Apr 2023 11:25:08 +0200 Johannes Berg wrote:
> On Fri, 2023-03-31 at 21:36 -0700, Jakub Kicinski wrote:
> >   
> > > +/* Note: due to dynamic registrations, access must be under RCU */
> > > +extern const struct drop_reason_list __rcu *
> > > +drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
> > > +
> > > +void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
> > > +				  const struct drop_reason_list *list);
> > > +void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);  
> > 
> > dropreason.h is included by skbuff.h because history, but I don't think
> > any of the new stuff must be visible in skbuff.h.
> > 
> > Could you make a new header, and put as much of this stuff there as
> > possible? Our future selves will thank us for shorter rebuild times..  
> 
> Sure. Not sure it'll make a big difference in rebuild, but we'll see :)
> 
> I ended up moving dropreason.h to dropreason-core.h first, that way we
> also have a naming scheme for non-core dropreason files should they
> become visible outside of the subsystem (i.e. mac80211 just has them
> internally).
> 
> Dunno, let me know if you prefer something else, I just couldn't come up
> with a non-confusing longer name for the new thing.

Sounds good.

> > Weak preference to also take the code out of skbuff.c but that's not as
> > important.  
> 
> I guess I can create a new dropreason.c, but is that worth it? It's only
> a few lines. Let me know, then I can resend.

It's hard to tell. Most additions to the core are small at the start so
we end up chucking all of them into a handful of existing source files.
And those files grow and grow. Splitting the later is extra work and
makes backports harder.

It's a game of predicting which code will likely grow into a reasonable
~500+ LoC at some point, and which code will not. I have the feeling
that dropreason code will grow. But yes, it's still fairly small, we 
can defer.

> > You To'd both wireless and netdev, who are you expecting to apply this?
> > :S  
> 
> Good question :)
> 
> The first patch (patches in v3) really should go through net-next I
> suppose, and I wouldn't mind if the other one did as well, it doesn't
> right now touch anything likely to change.

SG!
diff mbox series

Patch

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index c0a3ea806cd5..d7a134c108ad 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -339,10 +339,28 @@  enum skb_drop_reason {
 	 */
 	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
 	/**
-	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
-	 * used as a real 'reason'
-	 */
+	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
+	 * shouldn't be used as a real 'reason' - only for tracing code gen
+         */
 	SKB_DROP_REASON_MAX,
+
+	/** @SKB_DROP_REASON_SUBSYS_MASK: subsystem mask in drop reasons,
+	 * see &enum skb_drop_reason_subsys
+	 */
+	SKB_DROP_REASON_SUBSYS_MASK = 0xffff0000,
+};
+
+#define SKB_DROP_REASON_SUBSYS_SHIFT	16
+
+/**
+ * enum skb_drop_reason_subsys - subsystem tag for (extended) drop reasons
+ */
+enum skb_drop_reason_subsys {
+	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
+	SKB_DROP_REASON_SUBSYS_CORE,
+
+	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
+	SKB_DROP_REASON_SUBSYS_NUM
 };
 
 #define SKB_DR_INIT(name, reason)				\
@@ -358,6 +376,17 @@  enum skb_drop_reason {
 			SKB_DR_SET(name, reason);		\
 	} while (0)
 
-extern const char * const drop_reasons[];
+struct drop_reason_list {
+	const char * const *reasons;
+	size_t n_reasons;
+};
+
+/* Note: due to dynamic registrations, access must be under RCU */
+extern const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
+
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list);
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
 
 #endif
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 5a782d1d8fd3..c6c60dc75b2d 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -21,6 +21,7 @@ 
 #include <linux/workqueue.h>
 #include <linux/netlink.h>
 #include <linux/net_dropmon.h>
+#include <linux/bitfield.h>
 #include <linux/percpu.h>
 #include <linux/timer.h>
 #include <linux/bitops.h>
@@ -504,8 +505,6 @@  static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 	if (!nskb)
 		return;
 
-	if (unlikely(reason >= SKB_DROP_REASON_MAX || reason <= 0))
-		reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	cb = NET_DM_SKB_CB(nskb);
 	cb->reason = reason;
 	cb->pc = location;
@@ -552,9 +551,9 @@  static size_t net_dm_in_port_size(void)
 }
 
 #define NET_DM_MAX_SYMBOL_LEN 40
+#define NET_DM_MAX_REASON_LEN 50
 
-static size_t net_dm_packet_report_size(size_t payload_len,
-					enum skb_drop_reason reason)
+static size_t net_dm_packet_report_size(size_t payload_len)
 {
 	size_t size;
 
@@ -576,7 +575,7 @@  static size_t net_dm_packet_report_size(size_t payload_len,
 	       /* NET_DM_ATTR_PROTO */
 	       nla_total_size(sizeof(u16)) +
 	       /* NET_DM_ATTR_REASON */
-	       nla_total_size(strlen(drop_reasons[reason]) + 1) +
+	       nla_total_size(NET_DM_MAX_REASON_LEN + 1) +
 	       /* NET_DM_ATTR_PAYLOAD */
 	       nla_total_size(payload_len);
 }
@@ -610,6 +609,8 @@  static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 				     size_t payload_len)
 {
 	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
+	const struct drop_reason_list *list = NULL;
+	unsigned int subsys, subsys_reason;
 	char buf[NET_DM_MAX_SYMBOL_LEN];
 	struct nlattr *attr;
 	void *hdr;
@@ -627,9 +628,24 @@  static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 			      NET_DM_ATTR_PAD))
 		goto nla_put_failure;
 
+	rcu_read_lock();
+	subsys = u32_get_bits(cb->reason, SKB_DROP_REASON_SUBSYS_MASK);
+	if (subsys < SKB_DROP_REASON_SUBSYS_NUM)
+		list = rcu_dereference(drop_reasons_by_subsys[subsys]);
+	subsys_reason = cb->reason & ~SKB_DROP_REASON_SUBSYS_MASK;
+	if (!list ||
+	    subsys_reason >= list->n_reasons ||
+	    !list->reasons[subsys_reason] ||
+	    strlen(list->reasons[subsys_reason]) > NET_DM_MAX_REASON_LEN) {
+		list = rcu_dereference(drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_CORE]);
+		subsys_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	}
 	if (nla_put_string(msg, NET_DM_ATTR_REASON,
-			   drop_reasons[cb->reason]))
+			   list->reasons[subsys_reason])) {
+		rcu_read_unlock();
 		goto nla_put_failure;
+	}
+	rcu_read_unlock();
 
 	snprintf(buf, sizeof(buf), "%pS", cb->pc);
 	if (nla_put_string(msg, NET_DM_ATTR_SYMBOL, buf))
@@ -687,9 +703,7 @@  static void net_dm_packet_report(struct sk_buff *skb)
 	if (net_dm_trunc_len)
 		payload_len = min_t(size_t, net_dm_trunc_len, payload_len);
 
-	msg = nlmsg_new(net_dm_packet_report_size(payload_len,
-						  NET_DM_SKB_CB(skb)->reason),
-			GFP_KERNEL);
+	msg = nlmsg_new(net_dm_packet_report_size(payload_len), GFP_KERNEL);
 	if (!msg)
 		goto out;
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 050a875d09c5..d4b2a5cedbd4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -58,6 +58,7 @@ 
 #include <linux/scatterlist.h>
 #include <linux/errqueue.h>
 #include <linux/prefetch.h>
+#include <linux/bitfield.h>
 #include <linux/if_vlan.h>
 #include <linux/mpls.h>
 #include <linux/kcov.h>
@@ -122,11 +123,59 @@  EXPORT_SYMBOL(sysctl_max_skb_frags);
 
 #undef FN
 #define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
-const char * const drop_reasons[] = {
+static const char * const drop_reasons[] = {
 	[SKB_CONSUMED] = "CONSUMED",
 	DEFINE_DROP_REASON(FN, FN)
 };
-EXPORT_SYMBOL(drop_reasons);
+
+static const struct drop_reason_list drop_reasons_core = {
+	.reasons = drop_reasons,
+	.n_reasons = ARRAY_SIZE(drop_reasons),
+};
+
+const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
+	[SKB_DROP_REASON_SUBSYS_CORE] = &drop_reasons_core,
+};
+EXPORT_SYMBOL(drop_reasons_by_subsys);
+
+/**
+ * drop_reasons_register_subsys - register another drop reason subsystem
+ * @subsys: the subsystem to register, must not be the core
+ * @list: the list of drop reasons within the subsystem, must point to
+ *	a statically initialized list
+ */
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	/* must point to statically allocated memory, so INIT is OK */
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], list);
+}
+EXPORT_SYMBOL_GPL(drop_reasons_register_subsys);
+
+/**
+ * drop_reasons_unregister_subsys - unregister a drop reason subsystem
+ * @subsys: the subsystem to remove, must not be the core
+ *
+ * Note: This will synchronize_rcu() to ensure no users when it returns.
+ */
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], NULL);
+
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(drop_reasons_unregister_subsys);
 
 /**
  *	skb_panic - private function for out-of-line support
@@ -984,7 +1033,10 @@  bool __kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 	if (unlikely(!skb_unref(skb)))
 		return false;
 
-	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
+	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET ||
+			       u32_get_bits(reason,
+					    SKB_DROP_REASON_SUBSYS_MASK) >=
+				SKB_DROP_REASON_SUBSYS_NUM);
 
 	if (reason == SKB_CONSUMED)
 		trace_consume_skb(skb, __builtin_return_address(0));