Messages in this thread | | | Subject | Re: [PATCH] debugfs: fix potential infinite loop in debugfs_remove_recursive | From | "yukuai (C)" <> | Date | Thu, 14 Nov 2019 10:01:23 +0800 |
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Thanks for your explanation
On 2019/11/14 4:17, Steven Rostedt wrote: > On Thu, 31 Oct 2019 21:34:44 +0800 > yu kuai <yukuai3@huawei.com> wrote: > >> debugfs_remove_recursive uses list_empty to judge weather a dentry has >> any subdentry or not. This can lead to infinite loop when any subdir is in >> use. >> >> The problem was discoverd by the following steps in the console. >> 1. use debugfs_create_dir to create a dir and multiple subdirs(insmod); >> 2. cd to the subdir with depth not less than 2; >> 3. call debugfs_remove_recursive(rmmod). >> >> After removing the subdir, the infinite loop is triggered bucause > > s/bucause/because/ > >> debugfs_remove_recursive uses list_empty to judge if the current dir >> doesn't have any subdentry, if so, remove the current dir and which >> will never happen. >> >> Fix the problem by using simple_empty instead of list_empty. >> >> Fixes: 776164c1faac ('debugfs: debugfs_remove_recursive() must not rely on list_empty(d_subdirs)') >> Reported-by: chenxiang66@hisilicon.com >> Signed-off-by: yu kuai <yukuai3@huawei.com> >> --- >> fs/debugfs/inode.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c >> index 7b975db..42b28acc 100644 >> --- a/fs/debugfs/inode.c >> +++ b/fs/debugfs/inode.c >> @@ -773,8 +773,10 @@ void debugfs_remove_recursive(struct dentry *dentry) >> if (!simple_positive(child)) >> continue; >> >> - /* perhaps simple_empty(child) makes more sense */ >> - if (!list_empty(&child->d_subdirs)) { >> + /* use simple_empty to prevent infinite loop when any >> + * subdentry of child is in use >> + */ > > Nit, multi-line comments should be of the form: > > /* > * comment line 1 > * comment line 2 > */ > > Not > > /* comment line 1 > * comment line 2 > */ > > It's known that the networking folks like that method, but it's not > acceptable anywhere outside of networking. > Do you agree with that list_empty(&chile->d_subdirs) here is not appropriate? Since it can't skip the subdirs that is not simple_positive(simple_positive() will return false), which is the reason of infinite loop. >> + if (!simple_empty(child)) { > > Have you tried this with lockdep enabled? I'm thinking that you might > get a splat with holding parent->d_lock and simple_empty(child) taking > the child->d_lock. The locks are taken and released in the right order: take parent->d_lock take child->d_lock list_for_each_entry(c, &child->d_sundirs, d_child) take c->d_lock release c->d_lock release child->d_lock release parent->d_lock I don't see anything wrong, am I missing something?
Thanks Yu Kuai > > -- Steve > > >> spin_unlock(&parent->d_lock); >> inode_unlock(d_inode(parent)); >> parent = child; > > > . >
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