Hi Tetsuo, On 03/20/2019 07:42 PM, Tetsuo Handa wrote: > Hello. > > syzbot is sometimes generating corrupted reports like > https://syzkaller.appspot.com/text?tag=CrashLog&x=14f62a8b200000 . > > The report includes flood of global OOM killer invocations, and I suspect > that the reason of global OOM killer invocations is a lot of "blkid" processes > (invoked by uevent?) after manipulating loop devices with a lot of partitions. > > Can "blkid" be invoked asynchronously upon manipulating loop devices? I am not sure. Therefore I have tested on Ubuntu 16.04.5 VM running default 4.15.0-46-generic. 1. I hooked blkid by a proxy bash script. If blkid is involved, the related syslog will be printed to /var/log/syslog by 'logger': $ cat /sbin/blkid #!/bin/sh /sbin/blkid-bin $* logger "blkid $*" 2. Then I started to monitor udev messages via 'udevadm monitor'. 3. Finally, I did the test with below command set and there would be two partitions involved: # dd if=/dev/zero of=tmp.raw bs=1M count=100 oflag=direct # parted tmp.raw --script mklabel msdos mkpart primary 0% 50% mkpart primary 50% 100% # losetup -P /dev/loop0 tmp.raw # losetup -d /dev/loop0 Below are the udev messages captured during the test. For 'losetup -P /dev/loop0 tmp.raw': KERNEL[140.622809] change /devices/virtual/block/loop0 (block) KERNEL[140.640550] change /devices/virtual/block/loop0 (block) KERNEL[140.640601] add /devices/virtual/block/loop0/loop0p1 (block) KERNEL[140.640625] add /devices/virtual/block/loop0/loop0p2 (block) UDEV [140.676169] change /devices/virtual/block/loop0 (block) UDEV [140.692198] change /devices/virtual/block/loop0 (block) UDEV [140.701744] add /devices/virtual/block/loop0/loop0p1 (block) UDEV [140.724253] add /devices/virtual/block/loop0/loop0p2 (block) For 'losetup -d /dev/loop0': KERNEL[159.504382] change /devices/virtual/block/loop0 (block) KERNEL[159.504718] remove /devices/virtual/block/loop0/loop0p1 (block) KERNEL[159.504758] remove /devices/virtual/block/loop0/loop0p2 (block) UDEV [159.505807] change /devices/virtual/block/loop0 (block) UDEV [159.506201] remove /devices/virtual/block/loop0/loop0p1 (block) UDEV [159.507036] remove /devices/virtual/block/loop0/loop0p2 (block) There is NO blkid log printed to /var/log/syslog and I would assume blkid is not involved. This is just a test on ubuntu 16.04.5. I am not sure about the env of syzbot. Dongli Zhang
