On Wed, Apr 14, 2021 at 02:55:39PM +0200, Michal Hocko wrote: > On Wed 17-03-21 11:40:01, Feng Tang wrote: > > From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > > > Create a helper function (mpol_new_preferred_many()) which is usable > > both by the old, single-node MPOL_PREFERRED and the new > > MPOL_PREFERRED_MANY. > > > > Enforce the old single-node MPOL_PREFERRED behavior in the "new" > > version of mpol_new_preferred() which calls mpol_new_preferred_many(). > > > > v3: > > * fix a stack overflow caused by emty nodemask (Feng) > > > > Link: https://lore.kernel.org/r/20200630212517.308045-5-ben.widawsky@xxxxxxxxx > > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > Signed-off-by: Ben Widawsky <ben.widawsky@xxxxxxxxx> > > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > > --- > > mm/mempolicy.c | 21 +++++++++++++++++++-- > > 1 file changed, 19 insertions(+), 2 deletions(-) > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > index 1228d8e..6fb2cab 100644 > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -203,17 +203,34 @@ static int mpol_new_interleave(struct mempolicy *pol, const nodemask_t *nodes) > > return 0; > > } > > > > -static int mpol_new_preferred(struct mempolicy *pol, const nodemask_t *nodes) > > +static int mpol_new_preferred_many(struct mempolicy *pol, > > + const nodemask_t *nodes) > > { > > if (!nodes) > > pol->flags |= MPOL_F_LOCAL; /* local allocation */ > > Now you have confused me. I thought that MPOL_PREFERRED_MANY for NULL > nodemask will be disallowed as it is effectively MPOL_PREFERRED aka > MPOL_F_LOCAL. Or do I misread the code? I think you are right, with current code, the 'nodes' can't be NULL for MPOL_PREFERRED_MANY, we'll revisit this. And I have to admit that I am confused by the current logic for MPOL_PREFERRED, that the nodemask paramter changes between raw user input, empty nodes and NULL. Maybe the following patch can make it more clear, as it doesn't play the NULL nmask trick? --- diff --git a/mm/mempolicy.c b/mm/mempolicy.c index be160d4..9cabfca 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -200,12 +200,9 @@ static int mpol_new_interleave(struct mempolicy *pol, const nodemask_t *nodes) static int mpol_new_preferred(struct mempolicy *pol, const nodemask_t *nodes) { - if (!nodes) - pol->flags |= MPOL_F_LOCAL; /* local allocation */ - else if (nodes_empty(*nodes)) + if (nodes_empty(*nodes)) return -EINVAL; /* no allowed nodes */ - else - pol->v.preferred_node = first_node(*nodes); + pol->v.preferred_node = first_node(*nodes); return 0; } @@ -239,9 +236,11 @@ static int mpol_set_nodemask(struct mempolicy *pol, cpuset_current_mems_allowed, node_states[N_MEMORY]); VM_BUG_ON(!nodes); - if (pol->mode == MPOL_PREFERRED && nodes_empty(*nodes)) - nodes = NULL; /* explicit local allocation */ - else { + if (pol->mode == MPOL_PREFERRED && nodes_empty(*nodes)) { + /* explicit local allocation */ + pol->flags |= MPOL_F_LOCAL; + return 0; + } else { if (pol->flags & MPOL_F_RELATIVE_NODES) mpol_relative_nodemask(&nsc->mask2, nodes, &nsc->mask1); else @@ -254,10 +253,7 @@ static int mpol_set_nodemask(struct mempolicy *pol, cpuset_current_mems_allowed; } - if (nodes) - ret = mpol_ops[pol->mode].create(pol, &nsc->mask2); - else - ret = mpol_ops[pol->mode].create(pol, NULL); + ret = mpol_ops[pol->mode].create(pol, &nsc->mask2); return ret; } Thanks, Feng
