On Wed, 27 Feb 2019 19:38:47 +0100 Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 2/11/19 8:27 PM, Andrew Morton wrote: > > On Mon, 11 Feb 2019 10:02:45 -0800 <rcampbell@xxxxxxxxxx> wrote: > > > >> From: Ralph Campbell <rcampbell@xxxxxxxxxx> > >> > >> The system call, get_mempolicy() [1], passes an unsigned long *nodemask > >> pointer and an unsigned long maxnode argument which specifies the > >> length of the user's nodemask array in bits (which is rounded up). > >> The manual page says that if the maxnode value is too small, > >> get_mempolicy will return EINVAL but there is no system call to return > >> this minimum value. To determine this value, some programs search > >> /proc/<pid>/status for a line starting with "Mems_allowed:" and use > >> the number of digits in the mask to determine the minimum value. > >> A recent change to the way this line is formatted [2] causes these > >> programs to compute a value less than MAX_NUMNODES so get_mempolicy() > >> returns EINVAL. > >> > >> Change get_mempolicy(), the older compat version of get_mempolicy(), and > >> the copy_nodes_to_user() function to use nr_node_ids instead of > >> MAX_NUMNODES, thus preserving the defacto method of computing the > >> minimum size for the nodemask array and the maxnode argument. > >> > >> [1] http://man7.org/linux/man-pages/man2/get_mempolicy.2.html > >> [2] https://lore.kernel.org/lkml/1545405631-6808-1-git-send-email-longman@xxxxxxxxxx > > Please, the next time include linux-api and people involved in the previous > thread [1] into the CC list. Likely there should have been a Suggested-by: for > Alexander as well. > > >> > > > > Ugh, what a mess. > > I'm afraid it's even somewhat worse mess now. > > > For a start, that's a crazy interface. I wish that had been brought to > > our attention so we could have provided a sane way for userspace to > > determine MAX_NUMNODES. > > > > Secondly, 4fb8e5b89bcbbb ("include/linux/nodemask.h: use nr_node_ids > > (not MAX_NUMNODES) in __nodemask_pr_numnodes()") introduced a > > There's no such commit, that sha was probably from linux-next. The patch is > still in mmotm [1]. Luckily, I would say. Maybe Linus or some automation could > run some script to check for bogus Fixes tags before accepting patches? Ah, that's a relief. How about we just drop "include/linux/nodemask.h: use nr_node_ids (not MAX_NUMNODES) in __nodemask_pr_numnodes()" (https://ozlabs.org/~akpm/mmotm/broken-out/include-linux-nodemaskh-use-nr_node_ids-not-max_numnodes-in-__nodemask_pr_numnodes.patch)? It's just a cosmetic thing, really.
