Skip to content
Browse files

mm: fix hugetlb bug due to user_shm_unlock call

2.6.30's commit 8a0bdec 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>
  • Loading branch information...
1 parent 0257a0c commit 353d5c30c666580347515da609dd74a2b8e9b828 Hugh Dickins committed with torvalds Aug 24, 2009
Showing with 21 additions and 13 deletions.
  1. +12 −8 fs/hugetlbfs/inode.c
  2. +4 −2 include/linux/hugetlb.h
  3. +5 −3 ipc/shm.c
View
20 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 @@ struct file *hugetlb_file_setup(const char *name, size_t size, int acctflag)
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);
}
View
6 include/linux/hugetlb.h
@@ -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 */
View
8 ipc/shm.c
@@ -174,7 +174,7 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
shm_unlock(shp);
if (!is_file_hugepages(shp->shm_file))
shmem_lock(shp->shm_file, 0, shp->mlock_user);
- else
+ else if (shp->mlock_user)
user_shm_unlock(shp->shm_file->f_path.dentry->d_inode->i_size,
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;
no_id:
+ if (shp->mlock_user) /* shmflg & SHM_HUGETLB case */
+ user_shm_unlock(size, shp->mlock_user);
fput(file);
no_file:
security_shm_free(shp);

0 comments on commit 353d5c3

Please sign in to comment.
Something went wrong with that request. Please try again.