On Wed, Aug 2, 2017 at 6:50 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > Hi, > while doing something completely unrelated to selinux I've noticed a > really strange __GFP_NOMEMALLOC usage pattern in selinux, especially > GFP_ATOMIC | __GFP_NOMEMALLOC doesn't make much sense to me. GFP_ATOMIC > on its own allows to access memory reserves while the later flag tells > we cannot use memory reserves at all. The primary usecase for > __GFP_NOMEMALLOC is to override a global PF_MEMALLOC should there be a > need. > > It all leads to fa1aa143ac4a ("selinux: extended permissions for > ioctls") which doesn't explain this aspect so let me ask. Why is the > flag used at all? Moreover shouldn't GFP_ATOMIC be actually GFP_NOWAIT. > What makes this path important to access memory reserves? [NOTE: added the SELinux list to the CC line, please include that list when asking SELinux questions] The GFP_ATOMIC|__GFP_NOMEMALLOC use in SELinux appears to be limited to security/selinux/avc.c, and digging a bit, I'm guessing commit fa1aa143ac4a copied the combination from 6290c2c43973 ("selinux: tag avc cache alloc as non-critical") and the avc_alloc_node() function. I can't say that I'm an expert at the vm subsystem and the variety of different GFP_* flags, but your suggestion of moving to GFP_NOWAIT in security/selinux/avc.c seems reasonable and in keeping with the idea behind commit 6290c2c43973. -- paul moore security @ redhat -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>