On Mon, 23 Nov 2020, Andrew Morton wrote: > On Fri, 20 Nov 2020 17:55:22 -0800 syzbot <syzbot+e5a33e700b1dd0da20a2@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 03430750 Add linux-next specific files for 20201116 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=13f80e5e500000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=a1c4c3f27041fdb8 > > dashboard link: https://syzkaller.appspot.com/bug?extid=e5a33e700b1dd0da20a2 > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12f7bc5a500000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10934cf2500000 > > Alex, your series "per memcg lru lock" changed the vmscan code rather a > lot. Could you please take a look at that reproducer? Andrew, I promised I'd take a look at this syzreport too (though I think we're agreed by now that it has nothing to do with per-memcg lru_lock). I did try, but (unlike Alex) did not manage to get the reproducer to reproduce it. No doubt I did not try hard enough: I did rather lose interest after seeing that it appears to involve someone with CAP_SYS_ADMIN doing an absurdly large ioctl(BLKFRASET) on /dev/nullb0 ("Null test block driver" enabled via CONFIG_BLK_DEV_NULL_BLK=y: that I did enable) and faulting from it: presumably triggering an absurd amount of readahead. Cc'ing Matthew since he has a particular interest in readahead, and might be inspired to make some small safe change that would fix this, and benefit realistic cases too; but on the whole it didn't look worth worrying about - or at least not by me. Hugh > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+e5a33e700b1dd0da20a2@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > INFO: task syz-executor880:8534 can't die for more than 143 seconds. > > task:syz-executor880 state:R running task stack:25304 pid: 8534 ppid: 8504 flags:0x00004006 > > Call Trace: > > context_switch kernel/sched/core.c:4269 [inline] > > __schedule+0x890/0x2030 kernel/sched/core.c:5019 > > preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:5179 > > preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:40 > > __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline] > > _raw_spin_unlock_irq+0x3c/0x40 kernel/locking/spinlock.c:199 > > spin_unlock_irq include/linux/spinlock.h:404 [inline] > > shrink_inactive_list+0x4b1/0xce0 mm/vmscan.c:1974 > > shrink_list mm/vmscan.c:2167 [inline] > > shrink_lruvec+0x61b/0x11b0 mm/vmscan.c:2462 > > shrink_node_memcgs mm/vmscan.c:2650 [inline] > > shrink_node+0x839/0x1d60 mm/vmscan.c:2767 > > shrink_zones mm/vmscan.c:2970 [inline] > > do_try_to_free_pages+0x38b/0x1440 mm/vmscan.c:3025 > > try_to_free_pages+0x29f/0x720 mm/vmscan.c:3264 > > __perform_reclaim mm/page_alloc.c:4360 [inline] > > __alloc_pages_direct_reclaim mm/page_alloc.c:4381 [inline] > > __alloc_pages_slowpath.constprop.0+0x917/0x2510 mm/page_alloc.c:4785 > > __alloc_pages_nodemask+0x5f0/0x730 mm/page_alloc.c:4995 > > alloc_pages_current+0x191/0x2a0 mm/mempolicy.c:2271 > > alloc_pages include/linux/gfp.h:547 [inline] > > __page_cache_alloc mm/filemap.c:977 [inline] > > __page_cache_alloc+0x2ce/0x360 mm/filemap.c:962 > > page_cache_ra_unbounded+0x3a1/0x920 mm/readahead.c:216 > > do_page_cache_ra+0xf9/0x140 mm/readahead.c:267 > > do_sync_mmap_readahead mm/filemap.c:2721 [inline] > > filemap_fault+0x19d0/0x2940 mm/filemap.c:2809 > > __do_fault+0x10d/0x4d0 mm/memory.c:3623 > > do_shared_fault mm/memory.c:4071 [inline] > > do_fault mm/memory.c:4149 [inline] > > handle_pte_fault mm/memory.c:4385 [inline] > > __handle_mm_fault mm/memory.c:4520 [inline] > > handle_mm_fault+0x3033/0x55d0 mm/memory.c:4618 > > do_user_addr_fault+0x55b/0xba0 arch/x86/mm/fault.c:1377 > > handle_page_fault arch/x86/mm/fault.c:1434 [inline] > > exc_page_fault+0x9e/0x180 arch/x86/mm/fault.c:1490 > > asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580 > > RIP: 0033:0x400e71 > > Code: Unable to access opcode bytes at RIP 0x400e47. > > RSP: 002b:00007f8a5353fdc0 EFLAGS: 00010246 > > RAX: 6c756e2f7665642f RBX: 00000000006dbc38 RCX: 0000000000402824 > > RDX: 928195da81441750 RSI: 0000000000000000 RDI: 00000000006dbc30 > > RBP: 00000000006dbc30 R08: 0000000000000000 R09: 00007f8a53540700 > > R10: 00007f8a535409d0 R11: 0000000000000202 R12: 00000000006dbc3c > > R13: 00007ffe80747a5f R14: 00007f8a535409c0 R15: 0000000000000001 > > > > Showing all locks held in the system: > > 1 lock held by khungtaskd/1659: > > #0: ffffffff8b339ce0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6252 > > 1 lock held by kswapd0/2195: > > 1 lock held by kswapd1/2196: > > 1 lock held by in:imklog/8191: > > #0: ffff8880125b1270 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:932 > > 1 lock held by cron/8189: > > 2 locks held by syz-executor880/8502: > > 2 locks held by syz-executor880/8505: > > 2 locks held by syz-executor880/8507: > > 2 locks held by syz-executor880/11706: > > 2 locks held by syz-executor880/11709: > > 3 locks held by syz-executor880/12008: > > 2 locks held by syz-executor880/12015: > > > > ============================================= > > > > > > > > --- > > This report is generated by a bot. It may contain errors. > > See https://goo.gl/tpsmEJ for more information about syzbot. > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > syzbot can test patches for this issue, for details see: > > https://goo.gl/tpsmEJ#testing-patches
