ipc/sem.c: rewrite undo list locking
The attached patch:
- reverses the locking order of ulp->lock and sem_lock:
Previously, it was first ulp->lock, then inside sem_lock.
Now it's the other way around.
- converts the undo structure to rcu.
Benefits:
- With the old locking order, IPC_RMID could not kfree the undo structures.
The stale entries remained in the linked lists and were released later.
- The patch fixes a a race in semtimedop(): if both IPC_RMID and a semget() that
recreates exactly the same id happen between find_alloc_undo() and sem_lock,
then semtimedop() would access already kfree'd memory.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reviewed-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/sem.h b/include/linux/sem.h
index d425993..1b191c1 100644
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -78,6 +78,7 @@
#ifdef __KERNEL__
#include <asm/atomic.h>
+#include <linux/rcupdate.h>
struct task_struct;
@@ -114,7 +115,10 @@
* when the process exits.
*/
struct sem_undo {
- struct list_head list_proc; /* per-process list: all undos from one process */
+ struct list_head list_proc; /* per-process list: all undos from one process. */
+ /* rcu protected */
+ struct rcu_head rcu; /* rcu struct for sem_undo() */
+ struct sem_undo_list *ulp; /* sem_undo_list for the process */
struct list_head list_id; /* per semaphore array list: all undos for one array */
int semid; /* semaphore set identifier */
short * semadj; /* array of adjustments, one per semaphore */