On Mon, Dec 02, 2019 at 07:47:11AM +0100, Dmitry Vyukov wrote: > On Sun, Dec 1, 2019 at 1:04 AM Duncan Roe <duncan_roe@xxxxxxxxxxxxxxx> wrote: > > > > On Sat, Nov 30, 2019 at 04:53:12PM +0100, Dmitry Vyukov wrote: > > > On Sat, Nov 30, 2019 at 12:06 PM Duncan Roe <duncan_roe@xxxxxxxxxxxxxxx> wrote: > > > > > > syzbot has bisected this bug to: > > > > > > > > > > > > commit 77ef8f5177599efd0cedeb52c1950c1bd73fa5e3 > > > > > > Author: Chris Metcalf <cmetcalf@xxxxxxxxxx> > > > > > > Date: Mon Jan 25 20:05:34 2016 +0000 > > > > > > > > > > > > tile kgdb: fix bug in copy to gdb regs, and optimize memset > > > > > > > > > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1131bc0ee00000 > > > > > > start commit: f5b7769e Revert "debugfs: inode: debugfs_create_dir uses m.. > > > > > > git tree: upstream > > > > > > final crash: https://syzkaller.appspot.com/x/report.txt?x=1331bc0ee00000 > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1531bc0ee00000 > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=709f8187af941e84 > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=eaeb616d85c9a0afec7d > > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=177f898f800000 > > > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=147eb85f800000 > > > > > > > > > > > > Reported-by: syzbot+eaeb616d85c9a0afec7d@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > Fixes: 77ef8f517759 ("tile kgdb: fix bug in copy to gdb regs, and optimize > > > > > > memset") > > > > > > > > > > > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > > > > > > > > > Seriously? How can the commit in question (limited to arch/tile/kernel/kgdb.c) > > > > > possibly affect a bug that manages to produce a crash report with > > > > > RSP: 0018:ffffffff82e03eb8 EFLAGS: 00000282 > > > > > RAX: 0000000000000000 RBX: ffffffff82e00000 RCX: 0000000000000000 > > > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81088779 > > > > > RBP: ffffffff82e03eb8 R08: 0000000000000000 R09: 0000000000000001 > > > > > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > > > > > R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff82e00000 > > > > > FS: 0000000000000000(0000) GS:ffff88021fc00000(0000) knlGS:0000000000000000 > > > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > > > CR2: 000000c420447ff8 CR3: 0000000213184000 CR4: 00000000001406f0 > > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > > > in it? Unless something very odd has happened to tile, this crash has > > > > > been observed on 64bit x86; the names of registers alone are enough > > > > > to be certain of that. > > > > > > > > > > And the binaries produced by an x86 build should not be affected by any > > > > > changes in arch/tile; not unless something is very wrong with the build > > > > > system. It's not even that this commit has fixed an earlier bug that > > > > > used to mask the one manifested here - it really should have had zero > > > > > impact on x86 builds, period. > > > > > > > > > > So I'm sorry, but I'm calling bullshit. Something's quite wrong with > > > > > the bot - either its build system or the bisection process. > > > > > > > > The acid test would be: does reverting that commit make the problem go away? > > > > > > > > See, for example, https://bugzilla.kernel.org/show_bug.cgi?id=203935 > > > > > > > > Cheers ... Duncan. > > > > > > This is done as part of any bisection by definition, right? The test > > > was done on the previous commit (effectively this one reverted) and no > > > crash was observed. Otherwise bisection would have been pointed to a > > > different commit. > > > > > Agree that's what bisecting does. What I had in mind was to make a patch to > > remove the identified commit, and apply that to the most recent revision > > possible. Then see if that makes the problem go away. > > I wonder in what percent of cases: > 1. It gives signal different from reverting the commit in place. > 2. The revert can be cleanly applied to head. > 3. The revert does not introduce other bugs. > > For this to be worth doing, all these 3 should be reasonably high. I > can imagine 3 may be high (?), but I am not sure about 1 and 2. The whole arch/tile directory no longer exists, so the patch cannot be applied. If I had realised that earlier, I would not have posted at all. Sorry for the noise.
