On Tue, Nov 15, 2022, Andrew Morton wrote: > On Tue, 15 Nov 2022 08:23:44 -0800 syzbot <syzbot+644848628d5e12d5438c@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > Hello, > > > > syzbot found the following issue on: > > Thanks. > > > HEAD commit: f4bc5bbb5fef Merge tag 'nfsd-5.17-2' of git://git.kernel.o.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=16c683d8700000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=5707221760c00a20 > > dashboard link: https://syzkaller.appspot.com/bug?extid=644848628d5e12d5438c > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1691d2c2700000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16cde752700000 > > > > Bisection is inconclusive: the issue happens on the oldest tested release. > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=174c8174700000 > > final oops: https://syzkaller.appspot.com/x/report.txt?x=14cc8174700000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=10cc8174700000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+644848628d5e12d5438c@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > do_one_initcall+0x103/0x650 init/main.c:1300 > > do_initcall_level init/main.c:1373 [inline] > > do_initcalls init/main.c:1389 [inline] > > do_basic_setup init/main.c:1408 [inline] > > kernel_init_freeable+0x6b1/0x73a init/main.c:1613 > > kernel_init+0x1a/0x1d0 init/main.c:1502 > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > ------------[ cut here ]------------ > > kernel BUG at include/linux/memcontrol.h:470! > > That's > > VM_BUG_ON_FOLIO(folio_test_slab(folio), folio); > > in folio_memcg_rcu(). > > I'll cc the KVM list. Thanks! Saw this internally, was waiting for it to hit the lists. I haven't been able to repro the syzkaller test (abuses /dev/bus/usb crud), but I believe the issue is that KVM attempts to mark a kmalloc'd page as accessed. workingset_activation() doesn't expect this and invokes folio_memcg_rcu() on a SLAB page, which triggers the VM_BUG. I suspect this can be reproduced with a KVM selftest by mapping KVM's own vcpu->run memory into the guest. I'll give that a shot. In the meantime... #sys test https://github.com/sean-jc/linux.git x86/no_slab_accessed
