On Thu 18-04-19 15:50:39, Michal Koutny 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> Looks good to me. Please send both patches in one series once you get a review feedback from other people. > --- > kernel/sys.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 12df0e5434b8..bbce0f26d707 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2125,8 +2125,12 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = -EINVAL; > > - down_write(&mm->mmap_sem); > - vma = find_vma(mm, addr); > + /* > + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for > + * a) concurrent sys_brk, b) finding VMA for addr validation. > + */ > + down_read(&mm->mmap_sem); > + spin_lock(&mm->arg_lock); > > prctl_map.start_code = mm->start_code; > prctl_map.end_code = mm->end_code; > @@ -2185,6 +2189,7 @@ static int prctl_set_mm(int opt, unsigned long addr, > if (error) > goto out; > > + vma = find_vma(mm, addr); > switch (opt) { > /* > * If command line arguments and environment > @@ -2218,7 +2223,8 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = 0; > out: > - up_write(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > + up_read(&mm->mmap_sem); > return error; > } > > -- > 2.16.4 -- Michal Hocko SUSE Labs
