On Thu, Apr 18, 2019 at 03:50:39PM +0200, Michal Koutný wrote: > I learnt, it's, alas, too late to drop the non PRCTL_SET_MM_MAP calls > [1], so at least downgrade the write acquisition of mmap_sem as in the > patch below (that should be stacked on the previous one or squashed). > > Cyrill, you mentioned lock changes in [1] but the link seems empty. Is > it supposed to be [2]? That could be an alternative to this patch after > some refreshments and clarifications. > > > [1] https://lore.kernel.org/lkml/20190417165632.GC3040@xxxxxxxxxx/ > [2] https://lore.kernel.org/lkml/20180507075606.870903028@xxxxxxxxx/ > > ======== > > Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect > arg_start|end and env_start|end in mm_struct") we use arg_lock for > boundaries modifications. Synchronize prctl_set_mm with this lock and > keep mmap_sem for reading only (analogous to what we already do in > prctl_set_mm_map). > > Also, save few cycles by looking up VMA only after performing basic > arguments validation. > > Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx> As Laurent mentioned we might move vma lookup before the spinlock, but this might be done on top of the series.
