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cred: add get_cred_rcu()

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Sometimes we want to opportunistically get a
ref to a cred in an rcu_read_lock protected section.
get_task_cred() does this, and NFS does as similar thing
with its own credential structures.
To prepare for NFS converting to use 'struct cred' more
uniformly, define get_cred_rcu(), and use it in
get_task_cred().

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
NeilBrown 2018-12-03 11:30:30 +11:00 committed by Anna Schumaker
parent d89b22d46a
commit 97d0fb239c
2 changed files with 12 additions and 1 deletions
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11
include/linux/cred.h
View File

@ -252,6 +252,17 @@ static inline const struct cred *get_cred(const struct cred *cred)
return get_new_cred(nonconst_cred);
}
static inline const struct cred *get_cred_rcu(const struct cred *cred)
{
struct cred *nonconst_cred = (struct cred *) cred;
if (!cred)
return NULL;
if (!atomic_inc_not_zero(&nonconst_cred->usage))
return NULL;
validate_creds(cred);
return cred;
}
/**
* put_cred - Release a reference to a set of credentials
* @cred: The credentials to release

2
kernel/cred.c
View File

@ -195,7 +195,7 @@ const struct cred *get_task_cred(struct task_struct *task)
do {
cred = __task_cred((task));
BUG_ON(!cred);
} while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
} while (!get_cred_rcu(cred));
rcu_read_unlock();
return cred;