Messages in this thread Patch in this message | | | Date | Mon, 21 Apr 2014 18:47:34 -0400 | From | Pranith Kumar <> | Subject | Re: usage of rcu_dereference_raw |
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On Mon, Apr 21, 2014 at 6:03 PM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: >> do most of the uses of rcu_dereference_raw() need to be changed to use other >> dereference functions or are there cases where its usage is valid? > > The second call from iwl_op_mode_dvm_stop() -might- be valid. For it > to be valid, there must be a grace period between the time that the > field was made inaccessible to readers and the time that iwl_uninit_drv() > was called. Usually something like synchronize_rcu() waits for the > needed grace period.
So there are valid use cases of the rcu_dereference_raw() in scenarios where we can verify that a grace period has passed.
Thank you for the info. Mind adding it as a comment as in the patch below?
add comment for rcu_dereference_raw
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> --- include/linux/rcupdate.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 00a7fd6..af40a86 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -662,7 +662,13 @@ static inline void rcu_preempt_sleep_check(void) __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ __rcu) -#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ +/* rcu_dereference_raw() - rcu_dereference with no checking + * @p: The pointer to read, prior to dereferencing + * + * Use this to dereference a rcu pointer if you are sure that there exists a + * grace period between the time this pointer was made inaccessible to readers + */ +#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /* * The tracing infrastructure traces RCU (we want that), but unfortunately -- 1.7.9.5
-- Pranith
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