On Thu, Dec 12, 2019 at 7:34 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Dec 12, 2019 at 04:57:14PM +0100, Dmitry Vyukov wrote: > > > > Speaking of bisect hazards, I'd recommend to check how your bisect > > > went - the bug is definitely local to this commit and I really > > > wonder what had caused the bisect to go wrong in this particular > > > case. > > > > I did not get the relation of folding to bisection. Or you mean these > > are just separate things? > > Suppose instead of folding the fix in I would've done a followup commit > just with the fix. And left the branch in that form, eventually getting > it pulled into mainline. From that point on, *ANY* bisect stepping into > the first commit would've been thrown off. For ever and ever, since > once it's in mainline, it really won't go away. > > That's what folding avoids - accumulation of scar tissue, if you will. > Sure, there's enough cases when bug is found too late - it's already > in mainline or pulled into net-next or some other branch with similar > "no rebase, no reorder" policy. But if you look at the patchsets posted > on the lists and watch them from iteration to iteration, you'll see > a _lot_ of fix-folding. IME (both by my own practice and by watching > the patchsets posted by others) it outnumbers the cases when fix can't > be folded by quite a factor. I wouldn't be surprised if it was an > order of magnitude... > > Strict "never fold fixes" policy would've accelerated the accumulation > of bisect hazards in the mainline. And while useful bisect may be a lost > cause for CI bots, it isn't that for intelligent developers. Anything > that makes it more painful is not going to be welcome. Ah, I see. Yes, folding will help future bisections. In fact, an unfolded bug somewhere in kernel history is exactly what caused wrong result on bisection for this bug. Just in case, I did not propose to not do folding here (or anywhere else as far as I remember). Handling of folded fixes is documented in syzbot docs: https://goo.gl/tpsmEJ#rebuilt-treesamended-patches
