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Use atomic_t for ucounts reference counting

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The current implementation of the ucounts reference counter requires the
use of spin_lock. We're going to use get_ucounts() in more performance
critical areas like a handling of RLIMIT_SIGPENDING.

Now we need to use spin_lock only if we want to change the hashtable.

v10:
* Always try to put ucounts in case we cannot increase ucounts->count.
  This will allow to cover the case when all consumers will return
  ucounts at once.

v9:
* Use a negative value to check that the ucounts->count is close to
  overflow.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/94d1dbecab060a6b116b0a2d1accd8ca1bbb4f5f.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Alexey Gladkov
2021-04-22 14:27:10 +02:00
committed by Eric W. Biederman
parent 905ae01c4a
commit b6c3365289
2 changed files with 21 additions and 36 deletions
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4
include/linux/user_namespace.h
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@@ -95,7 +95,7 @@ struct ucounts {
struct hlist_node node;
struct user_namespace *ns;
kuid_t uid;
int count;
atomic_t count;
atomic_long_t ucount[UCOUNT_COUNTS];
};
@@ -107,7 +107,7 @@ void retire_userns_sysctls(struct user_namespace *ns);
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
struct ucounts *get_ucounts(struct ucounts *ucounts);
struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
void put_ucounts(struct ucounts *ucounts);
#ifdef CONFIG_USER_NS