On Wed 22-11-23 07:10:31, syzbot wrote: > syzbot found the following issue on: > > HEAD commit: 98b1cc82c4af Linux 6.7-rc2 > git tree: upstream > console+strace: https://syzkaller.appspot.com/x/log.txt?x=15e09a9f680000 > kernel config: https://syzkaller.appspot.com/x/.config?x=6ae1a4ee971a7305 > dashboard link: https://syzkaller.appspot.com/bug?extid=47479b71cdfc78f56d30 > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13c09a00e80000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=151d5320e80000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/39c6cdad13fc/disk-98b1cc82.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/5a77b5daef9b/vmlinux-98b1cc82.xz > kernel image: https://storage.googleapis.com/syzbot-assets/5e09ae712e0d/bzImage-98b1cc82.xz > > The issue was bisected to: > > commit 91562895f8030cb9a0470b1db49de79346a69f91 > Author: Jan Kara <jack@xxxxxxx> > Date: Fri Oct 13 12:13:50 2023 +0000 > > ext4: properly sync file size update after O_SYNC direct IO > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17d0f0c8e80000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=1430f0c8e80000 > console output: https://syzkaller.appspot.com/x/log.txt?x=1030f0c8e80000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+47479b71cdfc78f56d30@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO") > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 4481 at fs/ext4/file.c:391 ext4_dio_write_end_io+0x1db/0x220 fs/ext4/file.c:391 OK, so I could easily reproduce this which is good :). It took a bit longer to actually debug what's going on. In the end I've confirmed this is a false positive (the assertion isn't 100% reliable). What happens is that the IO end completion races with expanding truncate (which is not synchronized with DIO in any way) and the assertion sees a situation where i_disksize was updated but i_size not yet. This is mostly harmless but we better should complete the DIO only once we are sure truncate has updated the i_size as well. I'll think how to best do this. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
