diff options
| -rw-r--r-- | fs/kernfs/file.c | 51 |
1 files changed, 44 insertions, 7 deletions
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 316604c..bdd3885 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -54,6 +54,38 @@ static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn) return kn->attr.ops; } +/* + * As kernfs_seq_stop() is also called after kernfs_seq_start() or + * kernfs_seq_next() failure, it needs to distinguish whether it's stopping + * a seq_file iteration which is fully initialized with an active reference + * or an aborted kernfs_seq_start() due to get_active failure. The + * position pointer is the only context for each seq_file iteration and + * thus the stop condition should be encoded in it. As the return value is + * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable + * choice to indicate get_active failure. + * + * Unfortunately, this is complicated due to the optional custom seq_file + * operations which may return ERR_PTR(-ENODEV) too. kernfs_seq_stop() + * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or + * custom seq_file operations and thus can't decide whether put_active + * should be performed or not only on ERR_PTR(-ENODEV). + * + * This is worked around by factoring out the custom seq_stop() and + * put_active part into kernfs_seq_stop_active(), skipping it from + * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after + * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures + * that kernfs_seq_stop_active() is skipped only after get_active failure. + */ +static void kernfs_seq_stop_active(struct seq_file *sf, void *v) +{ + struct kernfs_open_file *of = sf->private; + const struct kernfs_ops *ops = kernfs_ops(of->kn); + + if (ops->seq_stop) + ops->seq_stop(sf, v); + kernfs_put_active(of->kn); +} + static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) { struct kernfs_open_file *of = sf->private; @@ -69,7 +101,11 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) ops = kernfs_ops(of->kn); if (ops->seq_start) { - return ops->seq_start(sf, ppos); + void *next = ops->seq_start(sf, ppos); + /* see the comment above kernfs_seq_stop_active() */ + if (next == ERR_PTR(-ENODEV)) + kernfs_seq_stop_active(sf, next); + return next; } else { /* * The same behavior and code as single_open(). Returns @@ -85,7 +121,11 @@ static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos) const struct kernfs_ops *ops = kernfs_ops(of->kn); if (ops->seq_next) { - return ops->seq_next(sf, v, ppos); + void *next = ops->seq_next(sf, v, ppos); + /* see the comment above kernfs_seq_stop_active() */ + if (next == ERR_PTR(-ENODEV)) + kernfs_seq_stop_active(sf, next); + return next; } else { /* * The same behavior and code as single_open(), always @@ -99,12 +139,9 @@ static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos) static void kernfs_seq_stop(struct seq_file *sf, void *v) { struct kernfs_open_file *of = sf->private; - const struct kernfs_ops *ops = kernfs_ops(of->kn); - if (ops->seq_stop) - ops->seq_stop(sf, v); - - kernfs_put_active(of->kn); + if (v != ERR_PTR(-ENODEV)) + kernfs_seq_stop_active(sf, v); mutex_unlock(&of->mutex); } |