On Sun, Dec 16, 2018 at 10:11:04PM -0800, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: d14b746c6c1c Add linux-next specific files for 20181214 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=13706347400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=1da6d2d18f803140 > dashboard link: https://syzkaller.appspot.com/bug?extid=5399ed0832693e29f392 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101032b3400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16534063400000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+5399ed0832693e29f392@xxxxxxxxxxxxxxxxxxxxxxxxx > > slab_pre_alloc_hook mm/slab.h:423 [inline] > slab_alloc mm/slab.c:3365 [inline] > kmem_cache_alloc+0x2c4/0x730 mm/slab.c:3539 > __d_alloc+0xc8/0xb90 fs/dcache.c:1599 > ------------[ cut here ]------------ > kernel BUG at fs/inode.c:1566! > d_alloc_anon fs/dcache.c:1698 [inline] > d_make_root+0x43/0xc0 fs/dcache.c:1885 > autofs_fill_super+0x6f1/0x1c30 fs/autofs/inode.c:273 Huh? BUG is in iput(), AFAICS, so the stack trace is rather misreported. iput() can be called by d_make_root(), provided that dentry allocation fails. So the most straightforward interpretation would be that we had an allocation failure (injected?), followed by iput() of the inode passed to d_make_root(). Which happened to find I_CLEAR in ->i_state of that inode somehow, which should be impossible short of seriously buggered inode refcounting somewhere - the inode has just been returned by new_inode(), which clears i_state, and it would have to have passed clear_inode() (i.e. has been through inode eviction) since then...
