[PATCH 3.16 063/366] ipc,shm: move BUG_ON check into shm_lock

Ben Hutchings
2018-10-14T15:25:41Z

From: Davidlohr Bueso <dave@stgolabs.net>

commit c5c8975b2eb4eb7604e8ce4f762987f56d2a96a2 upstream.

Upon every shm_lock call, we BUG_ON if an error was returned, indicating
racing either in idr or in shm_destroy. Move this logic into the locking.

[akpm@linux-foundation.org: simplify code]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
ipc/shm.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -155,8 +155,11 @@ static inline struct shmid_kernel *shm_l
{
struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);

- if (IS_ERR(ipcp))
- return (struct shmid_kernel *)ipcp;
+ /*
+ * We raced in the idr lookup or with shm_destroy(). Either way, the
+ * ID is busted.
+ */
+ BUG_ON(IS_ERR(ipcp));

return container_of(ipcp, struct shmid_kernel, shm_perm);
}
@@ -190,7 +193,6 @@ static void shm_open(struct vm_area_stru
struct shmid_kernel *shp;

shp = shm_lock(sfd->ns, sfd->id);
- BUG_ON(IS_ERR(shp));
shp->shm_atim = get_seconds();
shp->shm_lprid = task_tgid_vnr(current);
shp->shm_nattch++;
@@ -256,7 +258,6 @@ static void shm_close(struct vm_area_str
down_write(&shm_ids(ns).rwsem);
/* remove from the list of attaches of the shm segment */
shp = shm_lock(ns, sfd->id);
- BUG_ON(IS_ERR(shp));
shp->shm_lprid = task_tgid_vnr(current);
shp->shm_dtim = get_seconds();
shp->shm_nattch--;
@@ -1199,7 +1200,6 @@ out_fput:
out_nattch:
down_write(&shm_ids(ns).rwsem);
shp = shm_lock(ns, shmid);
- BUG_ON(IS_ERR(shp));
shp->shm_nattch--;
if (shm_may_destroy(ns, shp))
shm_destroy(ns, shp);