Commit 353d5c30 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm: fix hugetlb bug due to user_shm_unlock call

2.6.30's commit 8a0bdec1

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: default avatarStefan Huber <>
Signed-off-by: default avatarHugh Dickins <>
Tested-by: default avatarStefan Huber <>
Signed-off-by: default avatarLinus Torvalds <>
parent 0257a0c0
......@@ -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)) {
"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 @@ struct file *hugetlb_file_setup(const char *name, size_t size, int acctflag)
if (unlock_shm)
user_shm_unlock(size, user);
if (*user) {
user_shm_unlock(size, *user);
*user = NULL;
return ERR_PTR(error);
......@@ -10,6 +10,7 @@
#include <asm/tlbflush.h>
struct ctl_table;
struct user_struct;
int PageHuge(struct page *page);
......@@ -146,7 +147,8 @@ static inline struct hugetlbfs_sb_info *HUGETLBFS_SB(struct super_block *sb)
extern const struct file_operations hugetlbfs_file_operations;
extern struct vm_operations_struct hugetlb_vm_ops;
struct file *hugetlb_file_setup(const char *name, size_t, int);
struct file *hugetlb_file_setup(const char *name, size_t size, int acct,
struct user_struct **user);
int hugetlb_get_quota(struct address_space *mapping, long delta);
void hugetlb_put_quota(struct address_space *mapping, long delta);
......@@ -168,7 +170,7 @@ static inline void set_file_hugepages(struct file *file)
#define is_file_hugepages(file) 0
#define set_file_hugepages(file) BUG()
#define hugetlb_file_setup(name,size,acctflag) ERR_PTR(-ENOSYS)
#define hugetlb_file_setup(name,size,acct,user) ERR_PTR(-ENOSYS)
#endif /* !CONFIG_HUGETLBFS */
......@@ -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 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,
} 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);
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