On 09/15, Sasha Levin wrote: > > I've modified my tests to stress the exit path of processes with many vmas, > and hit the following NULL ptr deref (not sure if it's related to the original issue): I am shy to ask. Looks like I am the only stupid one who needs more info... > [1181047.935563] kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC KASAN Well, I know absolutely nothing about kasan, to the point I can't even unserstand where does this message come from. grep didn't help. But this doesn't matter... > [1181047.937223] Modules linked in: > [1181047.937772] CPU: 4 PID: 21912 Comm: trinity-c341 Not tainted 4.3.0-rc1-next-20150914-sasha-00043-geddd763-dirty #2554 > [1181047.939387] task: ffff8804195c8000 ti: ffff880433f00000 task.ti: ffff880433f00000 > [1181047.940533] RIP: unmap_vmas (mm/memory.c:1337) I do not know which tree/branch do you use. In Linus's tree mm/memory.c:1337 is struct mm_struct *mm = vma->vm_mm; but this doesn't match the asm below, > 0: 08 80 3c 02 00 0f or %al,0xf00023c(%rax) > 6: 85 22 test %esp,(%rdx) > 8: 01 00 add %eax,(%rax) > a: 00 48 8b add %cl,-0x75(%rax) > d: 43 rex.XB > e: 40 rex > f: 48 8d b8 c8 04 00 00 lea 0x4c8(%rax),%rdi > 16: 48 89 45 d0 mov %rax,-0x30(%rbp) > 1a: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax > 21: fc ff df > 24: 48 89 fa mov %rdi,%rdx > 27: 48 c1 ea 03 shr $0x3,%rdx > 2b:* 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction > 2f: 0f 85 ee 00 00 00 jne 0x123 > 35: 48 8b 45 d0 mov -0x30(%rbp),%rax > 39: 48 83 b8 c8 04 00 00 cmpq $0x0,0x4c8(%rax) > 40: 00 And I do not see anything similar in "objdump -d". So could you at least show mm/memory.c:1337 in your tree? Hmm. movabs $0xdffffc0000000000,%rax above looks suspicious, this looks like kasan_mem_to_shadow(). So perhaps this code was generated by kasan? (I can't check, my gcc is very old). Or what? Any chance you can tell us where exactly we hit NULL-deref in unmap_vmas? Oleg. -- 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>