From ce91f6ee5b3bbbad8caff61b1c46d845c8db19bf Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Thu, 7 Jun 2018 17:09:40 -0700 Subject: [PATCH] mm: kvmalloc does not fallback to vmalloc for incompatible gfp flags kvmalloc warned about incompatible gfp_mask to catch abusers (mostly GFP_NOFS) with an intention that this will motivate authors of the code to fix those. Linus argues that this just motivates people to do even more hacks like if (gfp == GFP_KERNEL) kvmalloc else kmalloc I haven't seen this happening much (Linus pointed to bucket_lock special cases an atomic allocation but my git foo hasn't found much more) but it is true that we can grow those in future. Therefore Linus suggested to simply not fallback to vmalloc for incompatible gfp flags and rather stick with the kmalloc path. Link: http://lkml.kernel.org/r/20180601115329.27807-1-mhocko@kernel.org Signed-off-by: Michal Hocko Suggested-by: Linus Torvalds Cc: Tom Herbert Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/bucket_locks.c | 5 +---- mm/util.c | 6 ++++-- 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/lib/bucket_locks.c b/lib/bucket_locks.c index 266a97c5708b..ade3ce6c4af6 100644 --- a/lib/bucket_locks.c +++ b/lib/bucket_locks.c @@ -30,10 +30,7 @@ int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *locks_mask, } if (sizeof(spinlock_t) != 0) { - if (gfpflags_allow_blocking(gfp)) - tlocks = kvmalloc(size * sizeof(spinlock_t), gfp); - else - tlocks = kmalloc_array(size, sizeof(spinlock_t), gfp); + tlocks = kvmalloc_array(size, sizeof(spinlock_t), gfp); if (!tlocks) return -ENOMEM; for (i = 0; i < size; i++) diff --git a/mm/util.c b/mm/util.c index c2d0a7cdb189..3351659200e6 100644 --- a/mm/util.c +++ b/mm/util.c @@ -391,7 +391,8 @@ EXPORT_SYMBOL(vm_mmap); * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is * preferable to the vmalloc fallback, due to visible performance drawbacks. * - * Any use of gfp flags outside of GFP_KERNEL should be consulted with mm people. + * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not + * fall back to vmalloc. */ void *kvmalloc_node(size_t size, gfp_t flags, int node) { @@ -402,7 +403,8 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node) * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables) * so the given set of flags has to be compatible. */ - WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); + if ((flags & GFP_KERNEL) != GFP_KERNEL) + return kmalloc_node(size, flags, node); /* * We want to attempt a large physically contiguous block first because -- 2.30.2