path: root/ipc
diff options
authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-08-24 16:30:28 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2009-08-24 12:53:01 -0700
commit353d5c30c666580347515da609dd74a2b8e9b828 (patch)
tree03cf3b5c0bc2ce08a12af303b141503ad833178f /ipc
parent0257a0c0c1997aac28420e784b3ef8f3ce17f093 (diff)
mm: fix hugetlb bug due to user_shm_unlock call
2.6.30's commit 8a0bdec194c21c8fdef840989d0d7b742bb5d4bc removed user_shm_lock() calls in hugetlb_file_setup() but left the user_shm_unlock call in shm_destroy(). In detail: Assume that can_do_hugetlb_shm() returns true and hence user_shm_lock() is not called in hugetlb_file_setup(). However, user_shm_unlock() is called in any case in shm_destroy() and in the following atomic_dec_and_lock(&up->__count) in free_uid() is executed and if up->__count gets zero, also cleanup_user_struct() is scheduled. Note that sched_destroy_user() is empty if CONFIG_USER_SCHED is not set. However, the ref counter up->__count gets unexpectedly non-positive and the corresponding structs are freed even though there are live references to them, resulting in a kernel oops after a lots of shmget(SHM_HUGETLB)/shmctl(IPC_RMID) cycles and CONFIG_USER_SCHED set. Hugh changed Stefan's suggested patch: can_do_hugetlb_shm() at the time of shm_destroy() may give a different answer from at the time of hugetlb_file_setup(). And fixed newseg()'s no_id error path, which has missed user_shm_unlock() ever since it came in 2.6.9. Reported-by: Stefan Huber <shuber2@gmail.com> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Tested-by: Stefan Huber <shuber2@gmail.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
1 files changed, 5 insertions, 3 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index 15dd238e5338..1bc4701ef4f0 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -174,7 +174,7 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
if (!is_file_hugepages(shp->shm_file))
shmem_lock(shp->shm_file, 0, shp->mlock_user);
- else
+ else if (shp->mlock_user)
fput (shp->shm_file);
@@ -369,8 +369,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
/* hugetlb_file_setup applies strict accounting */
if (shmflg & SHM_NORESERVE)
acctflag = VM_NORESERVE;
- file = hugetlb_file_setup(name, size, acctflag);
- shp->mlock_user = current_user();
+ file = hugetlb_file_setup(name, size, acctflag,
+ &shp->mlock_user);
} else {
* Do not allow no accounting for OVERCOMMIT_NEVER, even
@@ -410,6 +410,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
return error;
+ if (shp->mlock_user) /* shmflg & SHM_HUGETLB case */
+ user_shm_unlock(size, shp->mlock_user);

Privacy Policy