From 5f0d5a3ae7cff0d7fa943c199c3a2e44f23e1fac Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 18 Jan 2017 02:53:44 -0800 Subject: mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU A group of Linux kernel hackers reported chasing a bug that resulted from their assumption that SLAB_DESTROY_BY_RCU provided an existence guarantee, that is, that no block from such a slab would be reallocated during an RCU read-side critical section. Of course, that is not the case. Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire slab of blocks. However, there is a phrase for this, namely "type safety". This commit therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order to avoid future instances of this sort of confusion. Signed-off-by: Paul E. McKenney Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton Cc: Acked-by: Johannes Weiner Acked-by: Vlastimil Babka [ paulmck: Add comments mentioning the old name, as requested by Eric Dumazet, in order to help people familiar with the old name find the new one. ] Acked-by: David Rientjes --- Documentation/RCU/00-INDEX | 2 +- Documentation/RCU/rculist_nulls.txt | 6 +++--- Documentation/RCU/whatisRCU.txt | 3 ++- 3 files changed, 6 insertions(+), 5 deletions(-) (limited to 'Documentation/RCU') diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX index f773a264ae02..1672573b037a 100644 --- a/Documentation/RCU/00-INDEX +++ b/Documentation/RCU/00-INDEX @@ -17,7 +17,7 @@ rcu_dereference.txt rcubarrier.txt - RCU and Unloadable Modules rculist_nulls.txt - - RCU list primitives for use with SLAB_DESTROY_BY_RCU + - RCU list primitives for use with SLAB_TYPESAFE_BY_RCU rcuref.txt - Reference-count design for elements of lists/arrays protected by RCU rcu.txt diff --git a/Documentation/RCU/rculist_nulls.txt b/Documentation/RCU/rculist_nulls.txt index 18f9651ff23d..8151f0195f76 100644 --- a/Documentation/RCU/rculist_nulls.txt +++ b/Documentation/RCU/rculist_nulls.txt @@ -1,5 +1,5 @@ Using hlist_nulls to protect read-mostly linked lists and -objects using SLAB_DESTROY_BY_RCU allocations. +objects using SLAB_TYPESAFE_BY_RCU allocations. Please read the basics in Documentation/RCU/listRCU.txt @@ -7,7 +7,7 @@ Using special makers (called 'nulls') is a convenient way to solve following problem : A typical RCU linked list managing objects which are -allocated with SLAB_DESTROY_BY_RCU kmem_cache can +allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can use following algos : 1) Lookup algo @@ -96,7 +96,7 @@ unlock_chain(); // typically a spin_unlock() 3) Remove algo -------------- Nothing special here, we can use a standard RCU hlist deletion. -But thanks to SLAB_DESTROY_BY_RCU, beware a deleted object can be reused +But thanks to SLAB_TYPESAFE_BY_RCU, beware a deleted object can be reused very very fast (before the end of RCU grace period) if (put_last_reference_on(obj) { diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 5cbd8b2395b8..91c912e86915 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -925,7 +925,8 @@ d. Do you need RCU grace periods to complete even in the face e. Is your workload too update-intensive for normal use of RCU, but inappropriate for other synchronization mechanisms? - If so, consider SLAB_DESTROY_BY_RCU. But please be careful! + If so, consider SLAB_TYPESAFE_BY_RCU (which was originally + named SLAB_DESTROY_BY_RCU). But please be careful! f. Do you need read-side critical sections that are respected even though they are in the middle of the idle loop, during -- cgit v1.2.3