Prev: [PATCH]: Fix deadlock in USBIP driver (staging), linux-2.6.34-rc5
Next: perf-kvm.txt edits
From: Paul E. McKenney on 23 Apr 2010 21:30
On Fri, Apr 23, 2010 at 07:45:57PM -0500, Serge E. Hallyn wrote:
> So change the credentials documentation to make it clear that rcu
> read lock is required.

Very good!

Reviewed-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com>

> 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/
 | 
Pages: 1
Prev: [PATCH]: Fix deadlock in USBIP driver (staging), linux-2.6.34-rc5
Next: perf-kvm.txt edits