Re: [PATCH 2/2] kasan: Don't allocate page tables in kasan_release_vmalloc()

[Andrew Morton]

On Wed,  4 Dec 2019 23:45:34 +0300 Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:

> The purpose of kasan_release_vmalloc() is to unmap and deallocate shadow
> memory. The usage of apply_to_page_range() isn't suitable in that scenario
> because it allocates pages to fill missing page tables entries.
> This also cause sleep in atomic bug:
> 
> 	BUG: sleeping function called from invalid context at mm/page_alloc.c:4681
> 	in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15087, name:
> 
> 	Call Trace:
> 	 __dump_stack lib/dump_stack.c:77 [inline]
> 	 dump_stack+0x199/0x216 lib/dump_stack.c:118
> 	 ___might_sleep.cold.97+0x1f5/0x238 kernel/sched/core.c:6800
> 	 __might_sleep+0x95/0x190 kernel/sched/core.c:6753
> 	 prepare_alloc_pages mm/page_alloc.c:4681 [inline]
> 	 __alloc_pages_nodemask+0x3cd/0x890 mm/page_alloc.c:4730
> 	 alloc_pages_current+0x10c/0x210 mm/mempolicy.c:2211
> 	 alloc_pages include/linux/gfp.h:532 [inline]
> 	 __get_free_pages+0xc/0x40 mm/page_alloc.c:4786
> 	 __pte_alloc_one_kernel include/asm-generic/pgalloc.h:21 [inline]
> 	 pte_alloc_one_kernel include/asm-generic/pgalloc.h:33 [inline]
> 	 __pte_alloc_kernel+0x1d/0x200 mm/memory.c:459
> 	 apply_to_pte_range mm/memory.c:2031 [inline]
> 	 apply_to_pmd_range mm/memory.c:2068 [inline]
> 	 apply_to_pud_range mm/memory.c:2088 [inline]
> 	 apply_to_p4d_range mm/memory.c:2108 [inline]
> 	 apply_to_page_range+0x77d/0xa00 mm/memory.c:2133
> 	 kasan_release_vmalloc+0xa7/0xc0 mm/kasan/common.c:970
> 	 __purge_vmap_area_lazy+0xcbb/0x1f30 mm/vmalloc.c:1313
> 	 try_purge_vmap_area_lazy mm/vmalloc.c:1332 [inline]
> 	 free_vmap_area_noflush+0x2ca/0x390 mm/vmalloc.c:1368
> 	 free_unmap_vmap_area mm/vmalloc.c:1381 [inline]
> 	 remove_vm_area+0x1cc/0x230 mm/vmalloc.c:2209
> 	 vm_remove_mappings mm/vmalloc.c:2236 [inline]
> 	 __vunmap+0x223/0xa20 mm/vmalloc.c:2299
> 	 __vfree+0x3f/0xd0 mm/vmalloc.c:2356
> 	 __vmalloc_area_node mm/vmalloc.c:2507 [inline]
> 	 __vmalloc_node_range+0x5d5/0x810 mm/vmalloc.c:2547
> 	 __vmalloc_node mm/vmalloc.c:2607 [inline]
> 	 __vmalloc_node_flags mm/vmalloc.c:2621 [inline]
> 	 vzalloc+0x6f/0x80 mm/vmalloc.c:2666
> 	 alloc_one_pg_vec_page net/packet/af_packet.c:4233 [inline]
> 	 alloc_pg_vec net/packet/af_packet.c:4258 [inline]
> 	 packet_set_ring+0xbc0/0x1b50 net/packet/af_packet.c:4342
> 	 packet_setsockopt+0xed7/0x2d90 net/packet/af_packet.c:3695
> 	 __sys_setsockopt+0x29b/0x4d0 net/socket.c:2117
> 	 __do_sys_setsockopt net/socket.c:2133 [inline]
> 	 __se_sys_setsockopt net/socket.c:2130 [inline]
> 	 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:2130
> 	 do_syscall_64+0xfa/0x780 arch/x86/entry/common.c:294
> 	 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Why is this warning happening?  Some lock held?  If so, which one?

> Add kasan_unmap_page_range() which skips empty page table entries instead
> of allocating them.

Adding an open-coded range walker is unfortunate.  Did you consider
generalizing apply_to_page_range() for this purpose?  I did - it looks
messy.

Somewhat.  I guess adding another arg to
apply_to_p4d_range...apply_to_pte_range wouldn't kill us.  I wonder if
there would be other sites which could utilize the additional control.