diff options
| -rw-r--r-- | fs/debugfs/file.c | 55 | ||||
| -rw-r--r-- | fs/debugfs/inode.c | 36 | ||||
| -rw-r--r-- | fs/debugfs/internal.h | 8 |
3 files changed, 73 insertions, 26 deletions
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index bc3549c95574..65872340e301 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -53,6 +53,15 @@ const struct file_operations *debugfs_real_fops(const struct file *filp) { struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata; + if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT) { + /* + * Urgh, we've been called w/o a protecting + * debugfs_file_get(). + */ + WARN_ON(1); + return NULL; + } + return fsd->real_fops; } EXPORT_SYMBOL_GPL(debugfs_real_fops); @@ -74,9 +83,35 @@ EXPORT_SYMBOL_GPL(debugfs_real_fops); */ int debugfs_file_get(struct dentry *dentry) { - struct debugfs_fsdata *fsd = dentry->d_fsdata; + struct debugfs_fsdata *fsd; + void *d_fsd; + + d_fsd = READ_ONCE(dentry->d_fsdata); + if (!((unsigned long)d_fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)) { + fsd = d_fsd; + } else { + fsd = kmalloc(sizeof(*fsd), GFP_KERNEL); + if (!fsd) + return -ENOMEM; + + fsd->real_fops = (void *)((unsigned long)d_fsd & + ~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT); + refcount_set(&fsd->active_users, 1); + init_completion(&fsd->active_users_drained); + if (cmpxchg(&dentry->d_fsdata, d_fsd, fsd) != d_fsd) { + kfree(fsd); + fsd = READ_ONCE(dentry->d_fsdata); + } + } - /* Avoid starvation of removers. */ + /* + * In case of a successful cmpxchg() above, this check is + * strictly necessary and must follow it, see the comment in + * __debugfs_remove_file(). + * OTOH, if the cmpxchg() hasn't been executed or wasn't + * successful, this serves the purpose of not starving + * removers. + */ if (d_unlinked(dentry)) return -EIO; @@ -98,7 +133,7 @@ EXPORT_SYMBOL_GPL(debugfs_file_get); */ void debugfs_file_put(struct dentry *dentry) { - struct debugfs_fsdata *fsd = dentry->d_fsdata; + struct debugfs_fsdata *fsd = READ_ONCE(dentry->d_fsdata); if (refcount_dec_and_test(&fsd->active_users)) complete(&fsd->active_users_drained); @@ -109,10 +144,11 @@ static int open_proxy_open(struct inode *inode, struct file *filp) { struct dentry *dentry = F_DENTRY(filp); const struct file_operations *real_fops = NULL; - int r = 0; + int r; - if (debugfs_file_get(dentry)) - return -ENOENT; + r = debugfs_file_get(dentry); + if (r) + return r == -EIO ? -ENOENT : r; real_fops = debugfs_real_fops(filp); real_fops = fops_get(real_fops); @@ -233,10 +269,11 @@ static int full_proxy_open(struct inode *inode, struct file *filp) struct dentry *dentry = F_DENTRY(filp); const struct file_operations *real_fops = NULL; struct file_operations *proxy_fops = NULL; - int r = 0; + int r; - if (debugfs_file_get(dentry)) - return -ENOENT; + r = debugfs_file_get(dentry); + if (r) + return r == -EIO ? -ENOENT : r; real_fops = debugfs_real_fops(filp); real_fops = fops_get(real_fops); diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index f587aded46b5..9dca4da059b3 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -184,7 +184,10 @@ static const struct super_operations debugfs_super_operations = { static void debugfs_release_dentry(struct dentry *dentry) { - kfree(dentry->d_fsdata); + void *fsd = dentry->d_fsdata; + + if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)) + kfree(dentry->d_fsdata); } static struct vfsmount *debugfs_automount(struct path *path) @@ -344,35 +347,25 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode, { struct dentry *dentry; struct inode *inode; - struct debugfs_fsdata *fsd; - - fsd = kmalloc(sizeof(*fsd), GFP_KERNEL); - if (!fsd) - return NULL; if (!(mode & S_IFMT)) mode |= S_IFREG; BUG_ON(!S_ISREG(mode)); dentry = start_creating(name, parent); - if (IS_ERR(dentry)) { - kfree(fsd); + if (IS_ERR(dentry)) return NULL; - } inode = debugfs_get_inode(dentry->d_sb); - if (unlikely(!inode)) { - kfree(fsd); + if (unlikely(!inode)) return failed_creating(dentry); - } inode->i_mode = mode; inode->i_private = data; inode->i_fop = proxy_fops; - fsd->real_fops = real_fops; - refcount_set(&fsd->active_users, 1); - dentry->d_fsdata = fsd; + dentry->d_fsdata = (void *)((unsigned long)real_fops | + DEBUGFS_FSDATA_IS_REAL_FOPS_BIT); d_instantiate(dentry, inode); fsnotify_create(d_inode(dentry->d_parent), dentry); @@ -635,8 +628,17 @@ static void __debugfs_remove_file(struct dentry *dentry, struct dentry *parent) simple_unlink(d_inode(parent), dentry); d_delete(dentry); - fsd = dentry->d_fsdata; - init_completion(&fsd->active_users_drained); + + /* + * Paired with the closing smp_mb() implied by a successful + * cmpxchg() in debugfs_file_get(): either + * debugfs_file_get() must see a dead dentry or we must see a + * debugfs_fsdata instance at ->d_fsdata here (or both). + */ + smp_mb(); + fsd = READ_ONCE(dentry->d_fsdata); + if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT) + return; if (!refcount_dec_and_test(&fsd->active_users)) wait_for_completion(&fsd->active_users_drained); } diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h index 0eea99432840..cb1e8139c398 100644 --- a/fs/debugfs/internal.h +++ b/fs/debugfs/internal.h @@ -25,4 +25,12 @@ struct debugfs_fsdata { struct completion active_users_drained; }; +/* + * A dentry's ->d_fsdata either points to the real fops or to a + * dynamically allocated debugfs_fsdata instance. + * In order to distinguish between these two cases, a real fops + * pointer gets its lowest bit set. + */ +#define DEBUGFS_FSDATA_IS_REAL_FOPS_BIT BIT(0) + #endif /* _DEBUGFS_INTERNAL_H_ */ |