On 2018/09/05 16:22, Dmitry Vyukov wrote: > On Wed, Sep 5, 2018 at 5:41 AM, syzbot > <syzbot+f0fc7f62e88b1de99af3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: >> Hello, >> >> syzbot found the following crash on: >> >> HEAD commit: f2b6e66e9885 Add linux-next specific files for 20180904 >> git tree: linux-next >> console output: https://syzkaller.appspot.com/x/log.txt?x=1735dc92400000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=15ad48400e39c1b3 >> dashboard link: https://syzkaller.appspot.com/bug?extid=f0fc7f62e88b1de99af3 >> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >> CC: [adilger.kernel@xxxxxxxxx linux-ext4@xxxxxxxxxxxxxxx >> linux-kernel@xxxxxxxxxxxxxxx tytso@xxxxxxx] >> >> Unfortunately, I don't have any reproducer for this crash yet. >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> Reported-by: syzbot+f0fc7f62e88b1de99af3@xxxxxxxxxxxxxxxxxxxxxxxxx >> >> [ 7961] 0 7961 17585 8737 131072 0 0 >> syz-executor3 > > Hi Tetsuo, > > Maybe you know what are these repeated lines with numbers? > We started getting them on linux-next recently, also: > https://syzkaller.appspot.com/bug?extid=f8fa79b458bcae4d913d > They seem to cause various hangs/stalls. Yes, these lines are from the OOM killer. (Thus, if we can, I want to remove ext4 people before upstreaming this report.) dump_tasks mm/oom_kill.c:420 [inline] dump_header+0xf0d/0xf70 mm/oom_kill.c:450 oom_kill_process.cold.28+0x10/0x95a mm/oom_kill.c:953 out_of_memory+0xa88/0x1430 mm/oom_kill.c:1120 What is annoying is that one for_each_process() traversal with printk() is taking 52 seconds which is too long to do under RCU section. Under such situation, invoking the OOM killer for three times will exceed khungtaskd threshold 140 seconds. Was syzbot trying to test fork bomb situation? Anyway, we might need to introduce rcu_lock_break() like check_hung_uninterruptible_tasks() does... [ 999.629589] [ 16497] 0 16497 17585 8739 126976 0 0 syz-executor5 [ 1026.435955] [ 32764] 0 32764 17585 8739 126976 0 0 syz-executor5 [ 1026.445027] [ 311] 0 311 17585 8737 131072 0 0 syz-executor3 [ 1047.914324] [ 10315] 0 10315 17585 8271 126976 0 0 syz-executor0 [ 1047.923384] Out of memory: Kill process 4670 (syz-fuzzer) score 53 or sacrifice child [ 1047.931934] Killed process 5032 (syz-executor1) total-vm:70212kB, anon-rss:60kB, file-rss:0kB, shmem-rss:0kB [ 1047.988138] syz-executor2 invoked oom-killer: gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null), order=1, oom_score_adj=0 [ 1048.000015] syz-executor2 cpuset=syz2 mems_allowed=0 [ 1048.005199] CPU: 0 PID: 4700 Comm: syz-executor2 Not tainted 4.19.0-rc2-next-20180904+ #55 [ 1048.740679] [ 2347] 0 2347 278 186 32768 0 0 none [ 1051.319928] [ 16497] 0 16497 17585 8739 126976 0 0 syz-executor5 [ 1096.740878] [ 8841] 0 8841 17585 8232 126976 0 0 syz-executor5 [ 1078.140677] [ 32764] 0 32764 17585 8739 126976 0 0 syz-executor5 [ 1078.149807] [ 311] 0 311 17585 8737 131072 0 0 syz-executor3 [ 1096.740878] [ 8841] 0 8841 17585 8232 126976 0 0 syz-executor5 Also, another notable thing is that the backtrace for some reason includes [ 1048.211540] ? oom_killer_disable+0x3a0/0x3a0 line. Was syzbot testing process freezing functionality?
