[PATCH] ipc: convert invalid scenarios to use WARN_ON

[Davidlohr Bueso <dave@stgolabs.net>]

Considering Linus' past rants about the (ab)use of BUG in the kernel,
I took a look at how we deal with such calls in ipc. Given that any
errors or corruption in ipc code are most likely contained within
the set of processes participating in the broken mechanisms, there
aren't really many strong fatal system failure scenarios that would
require a BUG call. Also, if something is seriously wrong, ipc might
not be the place for such a BUG either.

1. For example, recently, a customer hit one of these BUG_ONs in shm
after failing shm_lock(). A busted ID imho does not merit a BUG_ON,
and WARN would have been better.

2. MSG_COPY functionality of posix msgrcv(2) for checkpoint/restore.
I don't see how we can hit this anyway -- at least it should be
IS_ERR. The 'copy' arg from do_msgrcv is always set by calling
prepare_copy() first and foremost. We could also probably drop
this check altogether. Either way, it does not merit a BUG_ON.

3. No ->fault() callback for the fs getting the corresponding page --
seems selfish to make the system unusable.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 ipc/msgutil.c | 2 +-
 ipc/shm.c     | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index 2b49159..71f448e 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -123,7 +123,7 @@ struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
 	size_t len = src->m_ts;
 	size_t alen;
 
-	BUG_ON(dst == NULL);
+	WARN_ON(dst == NULL);
 	if (src->m_ts > dst->m_ts)
 		return ERR_PTR(-EINVAL);
 
diff --git a/ipc/shm.c b/ipc/shm.c
index 06e5cf2..bcb1bad 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -159,7 +159,7 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
 	 * We raced in the idr lookup or with shm_destroy().  Either way, the
 	 * ID is busted.
 	 */
-	BUG_ON(IS_ERR(ipcp));
+	WARN_ON(IS_ERR(ipcp));
 
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
@@ -393,7 +393,7 @@ static int shm_mmap(struct file *file, struct vm_area_struct *vma)
 		return ret;
 	sfd->vm_ops = vma->vm_ops;
 #ifdef CONFIG_MMU
-	BUG_ON(!sfd->vm_ops->fault);
+	WARN_ON(!sfd->vm_ops->fault);
 #endif
 	vma->vm_ops = &shm_vm_ops;
 	shm_open(vma);
-- 
2.1.4