On Mon, Nov 11, 2019 at 07:16:29PM +1100, Matthew Bobrowski wrote: > On Fri, Nov 08, 2019 at 11:31:48AM +0100, Jan Kara wrote: > > On Thu 07-11-19 10:54:10, syzbot wrote: > > > syzbot found the following crash on: > > > > > > HEAD commit: c68c5373 Add linux-next specific files for 20191107 > > > git tree: linux-next > > > console output: https://syzkaller.appspot.com/x/log.txt?x=13d6bcfce00000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=742545dcdea21726 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=991400e8eba7e00a26e1 > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1529829ae00000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16a55c0ce00000 > > > > > > The bug was bisected to: > > > > > > commit b1b4705d54abedfd69dcdf42779c521aa1e0fbd3 > > > Author: Matthew Bobrowski <mbobrowski@xxxxxxxxxxxxxx> > > > Date: Tue Nov 5 12:01:37 2019 +0000 > > > > > > ext4: introduce direct I/O read using iomap infrastructure > > > > Hum, interesting and from the first looks the problem looks real. > > Deciphered reproducer is: > > > > int fd0 = open("./file0", O_RDWR | O_CREAT | O_EXCL | O_DIRECT, 0); > > int fd1 = open("./file0, O_RDONLY); > > write(fd0, "some_data...", 512); > > sendfile(fd0, fd1, NULL, 0x7fffffa7); > > -> this is interesting as it will result in reading data from 'file0' at > > offset X with buffered read and writing them with direct write to > > offset X+512. So this way we'll grow the file up to those ~2GB in > > 512-byte chunks. > > - not sure if we ever get there but the remainder of the reproducer is: > > fd2 = open("./file0", O_RDWR | O_CREAT | O_NOATIME | O_SYNC, 0); > > sendfile(fd2, fd0, NULL, 0xffffffff) > > -> doesn't seem too interesting as fd0 is at EOF so this shouldn't do > > anything. > > > > Matthew, can you have a look? > > Sorry Jan, I've been crazy busy lately and I'm out at training this > week. Let me take a look at this and see whether I can determine > what's happening here. > FYI, syzbot is still seeing this on linux-next. Also, a new thread was started to discuss this: https://lkml.kernel.org/linux-ext4/20191113180032.GB12013@xxxxxxxxxxxxxx/T/#u (Mentioning this in case anyone is following this thread only.) - Eric
