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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 /fs
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 'fs')
-rw-r--r--fs/hugetlbfs/inode.c20
1 files changed, 12 insertions, 8 deletions
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 941c8425c10..cb88dac8cca 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -935,26 +935,28 @@ static int can_do_hugetlb_shm(void)
return capable(CAP_IPC_LOCK) || in_group_p(sysctl_hugetlb_shm_group);
}
-struct file *hugetlb_file_setup(const char *name, size_t size, int acctflag)
+struct file *hugetlb_file_setup(const char *name, size_t size, int acctflag,
+ struct user_struct **user)
{
int error = -ENOMEM;
- int unlock_shm = 0;
struct file *file;
struct inode *inode;
struct dentry *dentry, *root;
struct qstr quick_string;
- struct user_struct *user = current_user();
+ *user = NULL;
if (!hugetlbfs_vfsmount)
return ERR_PTR(-ENOENT);
if (!can_do_hugetlb_shm()) {
- if (user_shm_lock(size, user)) {
- unlock_shm = 1;
+ *user = current_user();
+ if (user_shm_lock(size, *user)) {
WARN_ONCE(1,
"Using mlock ulimits for SHM_HUGETLB deprecated\n");
- } else
+ } else {
+ *user = NULL;
return ERR_PTR(-EPERM);
+ }
}
root = hugetlbfs_vfsmount->mnt_root;
@@ -996,8 +998,10 @@ out_inode:
out_dentry:
dput(dentry);
out_shm_unlock:
- if (unlock_shm)
- user_shm_unlock(size, user);
+ if (*user) {
+ user_shm_unlock(size, *user);
+ *user = NULL;
+ }
return ERR_PTR(error);
}