On Tue, 1 May 2018, Andrew Morton wrote: > On Tue, 24 Apr 2018 12:33:01 -0400 (EDT) Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > On Tue 24-04-18 11:30:40, Mikulas Patocka wrote: > > > > > > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > > > On Mon 23-04-18 20:25:15, Mikulas Patocka wrote: > > > > > > > > > > > Fixing __vmalloc code > > > > > > is easy and it doesn't require cooperation with maintainers. > > > > > > > > > > But it is a hack against the intention of the scope api. > > > > > > > > It is not! > > > > > > This discussion simply doesn't make much sense it seems. The scope API > > > is to document the scope of the reclaim recursion critical section. That > > > certainly is not a utility function like vmalloc. > > > > That 15-line __vmalloc bugfix doesn't prevent you (or any other kernel > > developer) from converting the code to the scope API. You make nonsensical > > excuses. > > > > Fun thread! > > Winding back to the original problem, I'd state it as > > - Caller uses kvmalloc() but passes the address into vmalloc-naive > DMA API and > > - Caller uses kvmalloc() but passes the address into kfree() > > Yes? > > If so, then... > > Is there a way in which, in the kvmalloc-called-kmalloc path, we can > tag the slab-allocated memory with a "this memory was allocated with > kvmalloc()" flag? I *think* there's extra per-object storage available > with suitable slab/slub debugging options? Perhaps we could steal one > bit from the redzone, dunno. > > If so then we can > > a) set that flag in kvmalloc() if the kmalloc() call succeeded > > b) check for that flag in the DMA code, WARN if it is set. > > c) in kvfree(), clear that flag before calling kfree() > > d) in kfree(), check for that flag and go WARN() if set. > > So both potential bugs are detected all the time, dependent upon > CONFIG_SLUB_DEBUG (and perhaps other slub config options). Yes, it would be good. You also need to check it in virt_to_phys(), virt_to_pfn(), __pa() and maybe some others. Mikulas
