Messages in this thread | | | Date | Tue, 16 Jul 2013 09:15:16 -0400 | From | Brian Foster <> | Subject | Re: [fuse-devel] [PATCH] fuse: fix occasional dentry leak when readdirplus is used |
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On 07/16/2013 06:39 AM, Niels de Vos wrote: > On Mon, Jul 15, 2013 at 04:08:22PM -0400, Brian Foster wrote: >> On 07/15/2013 08:59 AM, Niels de Vos wrote: ... > >>> --- >>> fs/fuse/dir.c | 4 +++- >>> 1 files changed, 3 insertions(+), 1 deletions(-) >>> >>> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c >>> index 0eda527..da67a15 100644 >>> --- a/fs/fuse/dir.c >>> +++ b/fs/fuse/dir.c >>> @@ -1246,7 +1246,9 @@ static int fuse_direntplus_link(struct file *file, >>> if (err) >>> goto out; >>> dput(dentry); >>> - dentry = NULL; >>> + } else if (dentry) { >>> + /* this dentry does not have a d_inode, just drop it */ >>> + dput(dentry); >>> } >> >> I'm not really familiar with the dcache code, but is it appropriate to >> also d_invalidate() the dentry in this case (as the previous code block >> does)? Perhaps Miklos or somebody more familiar with dcache can confirm... > > I do not *think* d_invalidate() is needed. The vmcores I have seem where > this BUG() happened, only have dentry->d_flags = 0x18 which translates > to (DCACHE_OP_DELETE | DCACHE_OP_PRUNE) and d_subdirs as an empty list. > d_invalidate() only calls __d_drop(), which only does something when the > dentry is hashed. >
I ran a little experiment to invoke a d_lookup() after the fuse_direntplus_link() function has done its work in this particular case. I do receive the newly allocated dentry.
Subsequently, I hacked __d_lookup_rcu() to continue iterating the list after finding an entry to check for duplicates and print a message. What I see is that after the dput() (via a subsequent lookup resulting from a getxattr call), the negative dentry is still hashed and on the list (my printk() kicks in after the existing d_unhashed() check). The flags for both dentries are (DCACHE_OP_REVALIDATE|DCACHE_REFERENCED|DCACHE_RCUACCESS). I'm not aware of the steps involved in the original reproducer, but the simple multi-mount test leads to this state. Running a d_invalidate() clears it up. So perhaps it's required in some cases and not all.
That said, some of those flags seem to simply specify whether a dentry op handler is defined for the particular operation or not.
> I am not sure if a dentry can be hashed, but still does not have a valid > non-NULL d_inode. If that is the case, d_invalidate() should indeed be > called. >
I'm not sure why it would need to have a valid inode. A dentry with a NULL inode is valid, no? I think the question is whether the above state (multiple, hashed dentries) can be valid for whatever reason. It certainly looks suspicious.
Brian
> Thanks, > Niels > >> Brian >> >>> >>> dentry = d_alloc(parent, &name); >>> >> >
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