Heap allocation doesn't properly detect out of memory error

[Rob Gries]

This problem comes up while testing scheduling.

On x86_64, we can create around 50 processes. If we then start a process cycle where each process creates the other, we hit a page fault and sometimes a double fault.

Error code: (empty)
ExceptionStack {
    instruction_pointer: 0x1116b6,
    code_segment: 0x8,
    cpu_flags: 0x6,
    stack_pointer: 0x40017940,
    stack_segment: 0x10
}
InterruptDescription {
    vector: 14,
    mnemonic: "#PF",
    description: "Page Fault",
    irqtype: "Fault",
    source: "Any memory reference."
}

Page fault while accessing 0x3fffffff

The instruction pointer points to a BTreeMap related function:

000000000013f130 <_ZN219_$LT$alloc..btree..node..Handle$LT$alloc..btree..node..NodeRef$LT$alloc..btree..node..marker..Mut$LT$$u27$a$GT$$C$$u20$K$C$$u20$V$C$$u20$alloc..btree..node..marker..Leaf$GT$$C$$u20$alloc..btree..node..marker..KV$GT$$GT$5split17h962bd6a453e19508E>:
  13f130:	55                   	push   %rbp
  13f131:	48 89 e5             	mov    %rsp,%rbp
  13f134:	48 81 ec a0 0f 00 00 	sub    $0xfa0,%rsp
  13f13b:	48 89 f8             	mov    %rdi,%rax
  13f13e:	48 8d 8d 60 f1 ff ff 	lea    -0xea0(%rbp),%rcx
  13f145:	c6 85 56 f9 ff ff 00 	movb   $0x0,-0x6aa(%rbp)
  13f14c:	c6 85 55 f9 ff ff 00 	movb   $0x0,-0x6ab(%rbp)
  13f153:	c6 85 57 f9 ff ff 00 	movb   $0x0,-0x6a9(%rbp)
  13f15a:	c6 85 54 f9 ff ff 00 	movb   $0x0,-0x6ac(%rbp)
  13f161:	c6 85 53 f9 ff ff 00 	movb   $0x0,-0x6ad(%rbp)
  13f168:	48 89 bd 50 f1 ff ff 	mov    %rdi,-0xeb0(%rbp)
  13f16f:	48 89 cf             	mov    %rcx,%rdi
  13f172:	48 89 85 48 f1 ff ff 	mov    %rax,-0xeb8(%rbp)
  13f179:	48 89 b5 40 f1 ff ff 	mov    %rsi,-0xec0(%rbp)
  13f180:	e8 1b 25 00 00       	callq  1416a0 <_ZN55_$LT$alloc..btree..node..LeafNode$LT$K$C$$u20$V$GT$$GT$3new17h54747f5e44c2a0b4E>
  13f185:	eb 0e                	jmp    13f195 <_ZN219_$LT$alloc..btree..node..Handle$LT$alloc..btree..node..NodeRef$LT$alloc..btree..node..marker..Mut$LT$$u27$a$GT$$C$$u20$K$C$$u20$V$C$$u20$alloc..btree..node..marker..Leaf$GT$$C$$u20$alloc..btree..node..marker..KV$GT$$GT$5split17h962bd6a453e19508E+0x65>