On Tue, Apr 09, 2019 at 07:36:00AM -0700, syzbot wrote: > Bisection is inconclusive: the first bad commit could be any of: [snip the useless pile] > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15e1fc2b200000 > start commit: [unknown > git tree: linux-next > dashboard link: https://syzkaller.appspot.com/bug?extid=5399ed0832693e29f392 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101032b3400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16534063400000 > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection If I'm not misreading the "crash report" there, it has injected an allocation failure in dentry allocation in d_make_root() from autofs_fill_super() ( root_inode = autofs_get_inode(s, S_IFDIR | 0755); root = d_make_root(root_inode); ) which has triggered iput() on the inode passed to d_make_root() (as it ought to). At which point it stepped into some BUG_ON() in fs/inode.c, but I've no idea which one it is - line numbers do not match anything in linux-next or in mainline. Reported line 1566 is if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) { in all of them; as the matter of fact, the diff in fs/inode.c between -next and mainline is empty. There is a BUG_ON() several lines prior, and in 4.20 it used to be line 1566, so _probably_ that's what it is. With that assumption, it's BUG_ON(inode->i_state & I_CLEAR); IOW, we'd got I_CLEAR in the inode passed to d_make_root() there. Which should not happen - the inode must have come from new_inode(), which gets it from new_inode_pseudo(), which zeroes ->i_state. And I_CLEAR is set only in clear_inode(). For autofs inodes that can come only from autofs_evict_inode(), called as ->evict() from evict_inode(). Which should never ever be called for inode with positive ->i_count... It might be memory corruption; it might be a dangling inode pointer somewhere, it might be something else. To get any further we really need a confirmation of the identity of triggered BUG_ON(). As an aside, your "sample crash reports" would've been much more useful if they went with commit SHA1 in question, especially when they contain line numbers.
