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author | Al Viro <viro@zeniv.linux.org.uk> | 2009-03-30 13:20:30 +0200 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2009-04-01 05:00:26 +0200 |
commit | 498052bba55ecaff58db6a1436b0e25bfd75a7ff (patch) | |
tree | bd3644ac60737e3733995a203acebd70cfd1b21b /fs/fs_struct.c | |
parent | Take fs_struct handling to new file (fs/fs_struct.c) (diff) | |
download | linux-498052bba55ecaff58db6a1436b0e25bfd75a7ff.tar.xz linux-498052bba55ecaff58db6a1436b0e25bfd75a7ff.zip |
New locking/refcounting for fs_struct
* all changes of current->fs are done under task_lock and write_lock of
old fs->lock
* refcount is not atomic anymore (same protection)
* its decrements are done when removing reference from current; at the
same time we decide whether to free it.
* put_fs_struct() is gone
* new field - ->in_exec. Set by check_unsafe_exec() if we are trying to do
execve() and only subthreads share fs_struct. Cleared when finishing exec
(success and failure alike). Makes CLONE_FS fail with -EAGAIN if set.
* check_unsafe_exec() may fail with -EAGAIN if another execve() from subthread
is in progress.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/fs_struct.c')
-rw-r--r-- | fs/fs_struct.c | 69 |
1 files changed, 49 insertions, 20 deletions
diff --git a/fs/fs_struct.c b/fs/fs_struct.c index 36e0a123bbf3..41cff72b377b 100644 --- a/fs/fs_struct.c +++ b/fs/fs_struct.c @@ -72,25 +72,27 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root) path_put(old_root); } -void put_fs_struct(struct fs_struct *fs) +void free_fs_struct(struct fs_struct *fs) { - /* No need to hold fs->lock if we are killing it */ - if (atomic_dec_and_test(&fs->count)) { - path_put(&fs->root); - path_put(&fs->pwd); - kmem_cache_free(fs_cachep, fs); - } + path_put(&fs->root); + path_put(&fs->pwd); + kmem_cache_free(fs_cachep, fs); } void exit_fs(struct task_struct *tsk) { - struct fs_struct * fs = tsk->fs; + struct fs_struct *fs = tsk->fs; if (fs) { + int kill; task_lock(tsk); + write_lock(&fs->lock); tsk->fs = NULL; + kill = !--fs->users; + write_unlock(&fs->lock); task_unlock(tsk); - put_fs_struct(fs); + if (kill) + free_fs_struct(fs); } } @@ -99,7 +101,8 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old) struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL); /* We don't need to lock fs - think why ;-) */ if (fs) { - atomic_set(&fs->count, 1); + fs->users = 1; + fs->in_exec = 0; rwlock_init(&fs->lock); fs->umask = old->umask; read_lock(&old->lock); @@ -114,28 +117,54 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old) int unshare_fs_struct(void) { - struct fs_struct *fsp = copy_fs_struct(current->fs); - if (!fsp) + struct fs_struct *fs = current->fs; + struct fs_struct *new_fs = copy_fs_struct(fs); + int kill; + + if (!new_fs) return -ENOMEM; - exit_fs(current); - current->fs = fsp; + + task_lock(current); + write_lock(&fs->lock); + kill = !--fs->users; + current->fs = new_fs; + write_unlock(&fs->lock); + task_unlock(current); + + if (kill) + free_fs_struct(fs); + return 0; } EXPORT_SYMBOL_GPL(unshare_fs_struct); /* to be mentioned only in INIT_TASK */ struct fs_struct init_fs = { - .count = ATOMIC_INIT(1), + .users = 1, .lock = __RW_LOCK_UNLOCKED(init_fs.lock), .umask = 0022, }; void daemonize_fs_struct(void) { - struct fs_struct *fs; + struct fs_struct *fs = current->fs; + + if (fs) { + int kill; + + task_lock(current); - exit_fs(current); /* current->fs->count--; */ - fs = &init_fs; - current->fs = fs; - atomic_inc(&fs->count); + write_lock(&init_fs.lock); + init_fs.users++; + write_unlock(&init_fs.lock); + + write_lock(&fs->lock); + current->fs = &init_fs; + kill = !--fs->users; + write_unlock(&fs->lock); + + task_unlock(current); + if (kill) + free_fs_struct(fs); + } } |