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

[Nicholas Piggin]

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@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
[np: move ifdefs into wrapper functions, slightly improve panic message]
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
---
 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;
+}
+
+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