On Tue, Jun 30, 2020 at 02:51:55PM +0000, Long Li wrote: > In the ARM32 environment with highmem enabled. Using flag of kmalloc() > with __GFP_HIGHMEM to allocate large memory, it will go through the > kmalloc_order() path and return NULL. The __GFP_HIGHMEM flag will > cause alloc_pages() to allocate highmem memory and pages cannot be > directly converted to a virtual address, kmalloc_order() will return > NULL and the page has been allocated. > > After modification, GFP_SLAB_BUG_MASK has been checked before > allocating pages, refer to the new_slab(). > > Signed-off-by: Long Li <lonuxli.64@xxxxxxxxx> > --- > > Changes in v2: > - patch is rebased againest "[PATCH] mm: Free unused pages in > kmalloc_order()" [1] > - check GFP_SLAB_BUG_MASK and generate warnings before alloc_pages > in kmalloc_order() > > [1] https://lkml.org/lkml/2020/6/27/16 > > mm/slab_common.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index a143a8c8f874..3548f4f8374b 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -27,6 +27,7 @@ > #include <trace/events/kmem.h> > > #include "slab.h" > +#include "internal.h" > > enum slab_state slab_state; > LIST_HEAD(slab_caches); > @@ -815,6 +816,15 @@ void *kmalloc_order(size_t size, gfp_t flags, unsigned int order) > void *ret = NULL; > struct page *page; > > + if (unlikely(flags & GFP_SLAB_BUG_MASK)) { > + gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK; > + > + flags &= ~GFP_SLAB_BUG_MASK; > + pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n", > + invalid_mask, &invalid_mask, flags, &flags); > + dump_stack(); > + } > + > flags |= __GFP_COMP; Oh, this is really good! I hadn't actually looked at how slab/slub handle GFP_SLAB_BUG_MASK. If you don't mind though, I would suggest that this code should all be in one place. Perhaps: gfp_t kmalloc_invalid_flags(gfp_t flags) { gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK; flags &= ~GFP_SLAB_BUG_MASK; pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n", invalid_mask, &invalid_mask, flags, &flags); dump_stack(); return flags; } and then call it from the three places? Also, the changelog could do with a bit of work. Perhaps: kmalloc cannot allocate memory from HIGHMEM. Allocating large amounts of memory currently bypasses the check and will simply leak the memory when page_address() returns NULL. To fix this, factor the GFP_SLAB_BUG_MASK check out of slab & slub, and call it from kmalloc_order() as well.
