Re: [PATCH -next/-mmotm] kernel/user.c: fix build when POLL not enabled

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Aug 04, 2021 at 02:59:23PM +1000, Nicholas Piggin wrote:
> Excerpts from Randy Dunlap's message of August 4, 2021 6:46 am:
> > Fix build errors in kernel/user.c when CONFIG_EPOLL is not set/enabled.
> > 
> > ../kernel/user.c: In function ‘free_user’:
> > ../kernel/user.c:141:30: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
> >   percpu_counter_destroy(&up->epoll_watches);
> >                               ^~~~~~~~~~~~~
> > In file included from ../include/linux/sched/user.h:7:0,
> >                  from ../kernel/user.c:17:
> > ../kernel/user.c: In function ‘alloc_uid’:
> > ../kernel/user.c:189:33: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
> >    if (percpu_counter_init(&new->epoll_watches, 0, GFP_KERNEL)) {
> >                                  ^
> > ../kernel/user.c:203:33: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
> >     percpu_counter_destroy(&new->epoll_watches);
> >                                  ^~~~~~~~~~~~~
> > In file included from ../include/linux/sched/user.h:7:0,
> >                  from ../kernel/user.c:17:
> > ../kernel/user.c: In function ‘uid_cache_init’:
> > ../kernel/user.c:225:37: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
> >   if (percpu_counter_init(&root_user.epoll_watches, 0, GFP_KERNEL))
> >                                      ^
> > Also fix type: "cpunter" -> "counter" in a panic message.
> 
> Gah, thanks Randy. The ifdefs aren't horrible but could I suggest a 
> slight tweak?
> 
> --
> From: Randy Dunlap <rdunlap@infradead.org>
> Subject: [PATCH] kernel/user.c: fix build when EPOLL not enabled
> 
> Fix build errors in kernel/user.c when CONFIG_EPOLL is not set/enabled.
> 
> ../kernel/user.c: In function ‘free_user’:
> ../kernel/user.c:141:30: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
>   percpu_counter_destroy(&up->epoll_watches);
>                               ^~~~~~~~~~~~~
> In file included from ../include/linux/sched/user.h:7:0,
>                  from ../kernel/user.c:17:
> ../kernel/user.c: In function ‘alloc_uid’:
> ../kernel/user.c:189:33: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
>    if (percpu_counter_init(&new->epoll_watches, 0, GFP_KERNEL)) {
>                                  ^
> ../kernel/user.c:203:33: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
>     percpu_counter_destroy(&new->epoll_watches);
>                                  ^~~~~~~~~~~~~
> In file included from ../include/linux/sched/user.h:7:0,
>                  from ../kernel/user.c:17:
> ../kernel/user.c: In function ‘uid_cache_init’:
> ../kernel/user.c:225:37: error: ‘struct user_struct’ has no member named ‘epoll_watches’; did you mean ‘nr_watches’?
>   if (percpu_counter_init(&root_user.epoll_watches, 0, GFP_KERNEL))
>                                      ^
> Also fix type: "cpunter" -"counter" in a panic message.
> 
> Fixes: e75b89477811 ("fs/epoll: use a per-cpu counter for user's watches count")
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> [np: move ifdefs into wrapper functions, slightly improve panic message]
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Nick Piggin <npiggin@gmail.com>
> Cc: Mark Brown <broonie@kernel.org>
> ---
>  kernel/user.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/user.c b/kernel/user.c
> index a2673f940506..57d53568cb33 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -129,6 +129,21 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
>  	return NULL;
>  }
>  
> +static int user_epoll_alloc(struct user_struct *up)
> +{
> +#ifdef CONFIG_EPOLL
> +	return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
> +#endif
> +	return 0;

#else
	return 0;
#endif

> +}
> +
> +static void user_epoll_free(struct user_struct *up)
> +{
> +#ifdef CONFIG_EPOLL
> +	percpu_counter_destroy(&up->epoll_watches);
> +#endif
> +}
> +
>  /* IRQs are disabled and uidhash_lock is held upon function entry.
>   * IRQ state (as stored in flags) is restored and uidhash_lock released
>   * upon function exit.
> @@ -138,7 +153,7 @@ static void free_user(struct user_struct *up, unsigned long flags)
>  {
>  	uid_hash_remove(up);
>  	spin_unlock_irqrestore(&uidhash_lock, flags);
> -	percpu_counter_destroy(&up->epoll_watches);
> +	user_epoll_free(up);
>  	kmem_cache_free(uid_cachep, up);
>  }
>  
> @@ -186,7 +201,7 @@ struct user_struct *alloc_uid(kuid_t uid)
>  
>  		new->uid = uid;
>  		refcount_set(&new->__count, 1);
> -		if (percpu_counter_init(&new->epoll_watches, 0, GFP_KERNEL)) {
> +		if (user_epoll_alloc(new)) {
>  			kmem_cache_free(uid_cachep, new);
>  			return NULL;
>  		}
> @@ -200,7 +215,7 @@ struct user_struct *alloc_uid(kuid_t uid)
>  		spin_lock_irq(&uidhash_lock);
>  		up = uid_hash_find(uid, hashent);
>  		if (up) {
> -			percpu_counter_destroy(&new->epoll_watches);
> +			user_epoll_free(new);
>  			kmem_cache_free(uid_cachep, new);
>  		} else {
>  			uid_hash_insert(new, hashent);
> @@ -222,8 +237,8 @@ static int __init uid_cache_init(void)
>  	for(n = 0; n < UIDHASH_SZ; ++n)
>  		INIT_HLIST_HEAD(uidhash_table + n);
>  
> -	if (percpu_counter_init(&root_user.epoll_watches, 0, GFP_KERNEL))
> -		panic("percpu cpunter alloc failed");
> +	if (user_epoll_alloc(&root_user))
> +		panic("root_user epoll percpu counter alloc failed");
>  
>  	/* Insert the root user immediately (init already runs as root) */
>  	spin_lock_irq(&uidhash_lock);
> -- 
> 2.23.0
>