From: Serge E. Hallyn on
So change the credentials documentation to make it clear that rcu
read lock is required.

Signed-off-by: Serge Hallyn <serue(a)>
Documentation/credentials.txt | 8 ++------
1 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/Documentation/credentials.txt b/Documentation/credentials.txt
index df03169..98a1e9e 100644
--- a/Documentation/credentials.txt
+++ b/Documentation/credentials.txt
@@ -408,9 +408,6 @@ This should be used inside the RCU read lock, as in the following example:

-A function need not get RCU read lock to use __task_cred() if it is holding a
-spinlock at the time as this implicitly holds the RCU read lock.
Should it be necessary to hold another task's credentials for a long period of
time, and possibly to sleep whilst doing so, then the caller should get a
reference on them using:
@@ -426,14 +423,13 @@ credentials, hiding the RCU magic from the caller:
uid_t task_uid(task) Task's real UID
uid_t task_euid(task) Task's effective UID

-If the caller is holding a spinlock or the RCU read lock at the time anyway,
+If the caller is holding the RCU read lock at the time anyway, then:


should be used instead. Similarly, if multiple aspects of a task's credentials
-need to be accessed, RCU read lock or a spinlock should be used, __task_cred()
+need to be accessed, RCU read lock should be used, __task_cred()
called, the result stored in a temporary pointer and then the credential
aspects called from that before dropping the lock. This prevents the
potentially expensive RCU magic from being invoked multiple times.

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