Re: [PATCH net] igmp: convert struct ip_sf_list to RCU

On Thu, Aug 27, 2026 at 10:13 AM kernel test robot <[email protected]> wrote:
>
> Hi Eric,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on net/main]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/igmp-convert-struct-ip_sf_list-to-RCU/20260826-115913
> base:   net/main
> patch link:    https://lore.kernel.org/r/20260826115913.3381537-1-edumazet%40google.com
> patch subject: [PATCH net] igmp: convert struct ip_sf_list to RCU
> config: i386-randconfig-062-20260827 (https://download.01.org/0day-ci/archive/20260827/[email protected]/config)
> compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
> sparse: v0.6.5-rc1
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260827/[email protected]/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <[email protected]>
> | Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
>
> sparse warnings: (new ones prefixed by >>)
>    net/ipv4/igmp.c: note: in included file (through include/linux/igmp.h):
>    include/uapi/linux/igmp.h:60:32: sparse: sparse: array of flexible structures
> >> net/ipv4/igmp.c:3114:13: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct ip_sf_list *psf @@     got struct ip_sf_list [noderef] __rcu *sf_next @@
>    net/ipv4/igmp.c:3114:13: sparse:     expected struct ip_sf_list *psf
>    net/ipv4/igmp.c:3114:13: sparse:     got struct ip_sf_list [noderef] __rcu *sf_next
> >> net/ipv4/igmp.c:3130:21: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct ip_sf_list *psf @@     got struct ip_sf_list [noderef] __rcu *sources @@
>    net/ipv4/igmp.c:3130:21: sparse:     expected struct ip_sf_list *psf
>    net/ipv4/igmp.c:3130:21: sparse:     got struct ip_sf_list [noderef] __rcu *sources
>    net/ipv4/igmp.c:3098:29: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct ip_sf_list *psf @@     got struct ip_sf_list [noderef] __rcu *sources @@
>    net/ipv4/igmp.c:3098:29: sparse:     expected struct ip_sf_list *psf
>    net/ipv4/igmp.c:3098:29: sparse:     got struct ip_sf_list [noderef] __rcu *sources
>    net/ipv4/igmp.c:3098:29: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct ip_sf_list *psf @@     got struct ip_sf_list [noderef] __rcu *sources @@
>    net/ipv4/igmp.c:3098:29: sparse:     expected struct ip_sf_list *psf
>    net/ipv4/igmp.c:3098:29: sparse:     got struct ip_sf_list [noderef] __rcu *sources
>

Thanks, I will squash in V2:

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 5516329c9caa5f6f3ec7a2f633bda5d1a16eb4ec..d56355aca79776575d93e338109b768f9acf2eaa
100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -3095,7 +3095,7 @@ static inline struct ip_sf_list
*igmp_mcf_get_first(struct seq_file *seq)
                im = rcu_dereference(idev->mc_list);
                if (likely(im)) {
                        spin_lock_bh(&im->lock);
-                       psf = im->sources;
+                       psf = pmc_dereference(im->sources, im);
                        if (likely(psf)) {
                                state->im = im;
                                state->idev = idev;
@@ -3111,7 +3111,7 @@ static struct ip_sf_list
*igmp_mcf_get_next(struct seq_file *seq, struct ip_sf_l
 {
        struct igmp_mcf_iter_state *state = igmp_mcf_seq_private(seq);

-       psf = psf->sf_next;
+       psf = pmc_dereference(psf->sf_next, state->im);
        while (!psf) {
                spin_unlock_bh(&state->im->lock);
                state->im = state->im->next;
@@ -3127,7 +3127,7 @@ static struct ip_sf_list
*igmp_mcf_get_next(struct seq_file *seq, struct ip_sf_l
                        state->im = rcu_dereference(state->idev->mc_list);
                }
                spin_lock_bh(&state->im->lock);
-               psf = state->im->sources;
+               psf = pmc_dereference(state->im->sources, state->im);
        }
 out:
        return psf;