Hi Michal, On Fri, Oct 21, 2016 at 08:46:02AM +0200, Michal Hocko wrote: > On Thu 20-10-16 23:39:39, Brian Norris wrote: > > I'm not sure the best way to report this, but the Chrome OS test > > infrastructure noticed some problems when testing the following patch > > backported to our 3.8 kernels: > > > > http://www.spinics.net/lists/stable/msg147998.html > > > > Specifically (if you can hold your nose and stand Gerrit), this change: > > > > https://chromium-review.googlesource.com/#/c/401041/
To be clear to any other readers, the above link has been updated with a new version. The version in question at the time of the original writing (and Michal's response) is preserved at this URL: https://chromium-review.googlesource.com/#/c/401041/2 > This is not correct. You have > https://chromium-review.googlesource.com/#/c/401041/2/mm/memory.c > > f ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, page, flags)) { > pte_unmap_unlock(ptep, ptl); > goto no_page; > } > > so you do a double unlock. See how my patch does > + if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, page, flags)) { > + pte_unmap_unlock(ptep, ptl); > + return NULL; > + } Wow, indeed we do have a double unlock. Sorry for not reading the backport more closely :( But thanks a bunch for the tip -- obvious in retrospect. Will give that a go. Also, I could have inferred that if it was so simple to crash the system, that there *had* to simply be something wrong with our patch, not with the patch you had (presumably tested and) posted. Sorry for the noise, and thanks again. Brian
