fix idr_find() locking
This is a patch that fixes the way idr_find() used to be called in ipc_lock():
in all the paths that don't imply an update of the ipcs idr, it was called
without the idr tree being locked.
The changes are:
. in ipc_ids, the mutex has been changed into a reader/writer semaphore.
. ipc_lock() now takes the mutex as a reader during the idr_find().
. a new routine ipc_lock_down() has been defined: it doesn't take the
mutex, assuming that it is being held by the caller. This is the routine
that is now called in all the update paths.
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/util.h b/ipc/util.h
index 99414a3..bd47687 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -32,7 +32,7 @@
int in_use;
unsigned short seq;
unsigned short seq_max;
- struct mutex mutex;
+ struct rw_semaphore rw_mutex;
struct idr ipcs_idr;
};
@@ -81,8 +81,10 @@
#define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
-/* must be called with ids->mutex acquired.*/
+/* must be called with ids->rw_mutex acquired for writing */
int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
+
+/* must be called with ids->rw_mutex acquired for reading */
int ipc_get_maxid(struct ipc_ids *);
/* must be called with both locks acquired. */
@@ -107,6 +109,11 @@
void ipc_rcu_getref(void *ptr);
void ipc_rcu_putref(void *ptr);
+/*
+ * ipc_lock_down: called with rw_mutex held
+ * ipc_lock: called without that lock held
+ */
+struct kern_ipc_perm *ipc_lock_down(struct ipc_ids *, int);
struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);
@@ -155,6 +162,23 @@
rcu_read_unlock();
}
+static inline struct kern_ipc_perm *ipc_lock_check_down(struct ipc_ids *ids,
+ int id)
+{
+ struct kern_ipc_perm *out;
+
+ out = ipc_lock_down(ids, id);
+ if (IS_ERR(out))
+ return out;
+
+ if (ipc_checkid(ids, out, id)) {
+ ipc_unlock(out);
+ return ERR_PTR(-EIDRM);
+ }
+
+ return out;
+}
+
static inline struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids,
int id)
{
