On Wed, 27 Feb 2019 19:38:47 +0100 Vlastimil Babka vbabka@suse.cz wrote:
On 2/11/19 8:27 PM, Andrew Morton wrote:
On Mon, 11 Feb 2019 10:02:45 -0800 rcampbell@nvidia.com wrote:
From: Ralph Campbell rcampbell@nvidia.com
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@redhat...
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_nod... It's just a cosmetic thing, really.