Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount root fs

On Tue, Jan 20, 2015 at 06:44:34PM -0800, Guenter Roeck wrote: Just what is lib/modules/3.9.2 doing there? In any case, I think I have at least a plausible direction for digging. Look: struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, unsigned int lookup_flags) { struct filename *tmp = getname(pathname); struct dentry *res; if (IS_ERR(tmp)) return ERR_CAST(tmp); res = kern_path_create(dfd, tmp->name, path, lookup_flags); struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, unsigned int lookup_flags) { struct dentry *dentry = ERR_PTR(-EEXIST); struct nameidata nd; int err2; int error; bool is_dir = (lookup_flags & LOOKUP_DIRECTORY); /* * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any * other flags passed in are ignored! */ lookup_flags &= LOOKUP_REVAL; error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd); static int do_path_lookup(int dfd, const char *name, unsigned int flags, struct nameidata *nd) { int retval; struct filename *filename; filename = getname_kernel(name); if (unlikely(IS_ERR(filename))) return PTR_ERR(filename); retval = filename_lookup(dfd, filename, flags, nd); and we have done getname_kernel() on the name->name of result of getname(). At the very least, it's pointless - we already *have* struct filename for that sucker. Now, it shouldn't have screwed the things up - it would better not, anyway, since we might legitimately have two identical pathname among the syscall arguments. However, let's see if this (on top of linux-next, in addition to the same printks) changes behaviour: diff --git a/fs/namei.c b/fs/namei.c index 323957f..c7d107c 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3314,7 +3314,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, return file; } -struct dentry *kern_path_create(int dfd, const char *pathname, +static struct dentry *__kern_path_create(int dfd, struct filename *name, struct path *path, unsigned int lookup_flags) { struct dentry *dentry = ERR_PTR(-EEXIST); @@ -3329,7 +3329,7 @@ struct dentry *kern_path_create(int dfd, const char *pathname, */ lookup_flags &= LOOKUP_REVAL; - error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd); + error = filename_lookup(dfd, name, LOOKUP_PARENT|lookup_flags, &nd); if (error) return ERR_PTR(error); @@ -3383,6 +3383,19 @@ out: path_put(&nd.path); return dentry; } + +struct dentry *kern_path_create(int dfd, const char *pathname, + struct path *path, unsigned int lookup_flags) +{ + struct filename *filename = getname_kernel(pathname); + struct dentry *res = ERR_CAST(filename); + + if (!IS_ERR(filename)) { + res = __kern_path_create(dfd, filename, path, lookup_flags); + putname(filename); + } + return res; +} EXPORT_SYMBOL(kern_path_create); void done_path_create(struct path *path, struct dentry *dentry) @@ -3401,7 +3414,7 @@ struct dentry *user_path_create(int dfd, const char __user *pathname, struct dentry *res; if (IS_ERR(tmp)) return ERR_CAST(tmp); - res = kern_path_create(dfd, tmp->name, path, lookup_flags); + res = __kern_path_create(dfd, tmp, path, lookup_flags); putname(tmp); return res; }