Commit-ID: 2c4ac34bc2d97f056ed3c43fa03c0737fae46fb6 Gitweb: http://git.kernel.org/tip/2c4ac34bc2d97f056ed3c43fa03c0737fae46fb6 Author: Jason A. Donenfeld <Jason@xxxxxxxxx> AuthorDate: Tue, 11 Aug 2015 14:26:33 +0200 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Tue, 6 Oct 2015 11:22:43 -0700 documentation: Correct doc to use rcu_dereference_protected As there is lots of misinformation and outdated information on the Internet about nearly all topics related to the kernel, I thought it would be best if I based my RCU code on the guidelines of the examples in the Documentation/ tree of the latest kernel. One thing that stuck out when reading the whatisRCU.txt document was, "interesting how we don't need any function to dereference rcu protected pointers when doing updates if a lock is held. I wonder how static analyzers will work with that." Then, a few weeks later, upon discovering sparse's __rcu support, I ran it over my code, and lo and behold, things weren't done right. Examining other RCU usages in the kernel reveal consistent usage of rcu_dereference_protected, passing in lockdep_is_held as the conditional. So, this patch adds that idiom to the documentation, so that others ahead of me won't endure the same exercise. Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> --- Documentation/RCU/whatisRCU.txt | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index adc2184..dc49c67 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -364,7 +364,7 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt. }; DEFINE_SPINLOCK(foo_mutex); - struct foo *gbl_foo; + struct foo __rcu *gbl_foo; /* * Create a new struct foo that is the same as the one currently @@ -386,7 +386,7 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt. new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL); spin_lock(&foo_mutex); - old_fp = gbl_foo; + old_fp = rcu_dereference_protected(gbl_foo, lockdep_is_held(&foo_mutex)); *new_fp = *old_fp; new_fp->a = new_a; rcu_assign_pointer(gbl_foo, new_fp); @@ -487,7 +487,7 @@ The foo_update_a() function might then be written as follows: new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL); spin_lock(&foo_mutex); - old_fp = gbl_foo; + old_fp = rcu_dereference_protected(gbl_foo, lockdep_is_held(&foo_mutex)); *new_fp = *old_fp; new_fp->a = new_a; rcu_assign_pointer(gbl_foo, new_fp); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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