[PATCH] Documentation/cred.txt: spinlock no longer implies rcu_read_lock
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From: Serge E. Hallyn on 23 Apr 2010 20:50 So change the credentials documentation to make it clear that rcu read lock is required. Signed-off-by: Serge Hallyn <serue(a)us.ibm.com> --- 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, -then: +If the caller is holding the RCU read lock at the time anyway, then: __task_cred(task)->uid __task_cred(task)->euid 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. -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |