On Jun 2, 2016, at 11:37 PM, Al Viro wrote: > On Thu, Jun 02, 2016 at 06:46:08PM -0400, Oleg Drokin wrote: >> Hello! >> >> I just came across a bug (trying to run some Lustre test scripts against >> NFS, while hunting for another nfsd bug) >> that seems to be present since at least 2014 that lets users crash nfs >> client locally. > >>> * Cluster filesystems may call this function with a negative, hashed dentry. >>> * In that case, we know that the inode will be a regular file, and also this >>> * will only occur during atomic_open. So we need to check for the dentry >>> * being already hashed only in the final case. > > Comment is long obsolete and should've been removed. "Cluster filesystem" > in question was GFS2 and it had been dealt with there. Mea culpa - should've > removed the comment as soon as that was done.
Oh, ok. I assumed it was still valid, esp. considering the issue at hand where what it describes actually happens and NFS is also a cluster filesystem of sorts ;) >> The problem was there at least since 3.10 it appears where the fs/nfs/dir.c >> code >> was calling d_materialise_unique() that did require the dentry to be >> unhashed. >> >> Not sure how this was not hit earlier. The crash looks like this (I added >> a printk to ensure this is what is going on indeed and not some other weird >> race): > >> [ 64.489326] Calling into d_splice_alias with hashed dentry, >> dentry->d_inode (null) inode ffff88010f500c70 > > Which of the call sites had that been and how does one reproduce that fun? > If you feel that posting a reproducer in the open is a bad idea, just send > it off-list... This is fs/nfs/dir.c::nfs_lookup() right after no_entry label. I'll send you the scripts with instructions separately for now.
