On Sat, Oct 23, 2021 at 9:35 AM syzbot <syzbot+75639e6a0331cd61d3e2@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > syzbot found the following issue on: > > HEAD commit: 9c0c4d24ac00 Merge tag 'block-5.15-2021-10-22' of git://gi.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=115a0328b00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=59f3ef2b4077575 > dashboard link: https://syzkaller.appspot.com/bug?extid=75639e6a0331cd61d3e2 > compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13a035c2b00000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14ae869f300000 > > The issue was bisected to: > > commit 110860541f443f950c1274f217a1a3e298670a33 I think that commit is actually just buggy. "secretmem_users" is not actually a reference count. There's no "magic happens when it goes down to zero". It's purely a count of the number of existing users, and incrementing it from zero is not a probolem at all - it is in fact expected. Sure, zero means "we can hibernate", so zero and overflow are somewhat special, but not special enough to cause these kinds of issues. I have reverted this commit in my tree, because honestly, the whole "try to overflow exactly, and hibernate" threat model just isn't worth this all. If people really care, I can suggest - use "atomic_long_t" instead. Let's face it, 32-bit isn't interesting any more, and 64-bit doesn't overflow. - make up some new "atomic_inc_nooverflow()" thing or whatever. but for now this is just reverted. Linus
