Do not sleep in vm_wait() if pagedaemon is not yet started.

[kib]

Summary

Panic instead. Example of the change in action, for damaged kernel binary file:

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FreeBSD 12.0-CURRENT #18 r308105+56db418(lld-buildworld)-dirty: Wed Nov  2 10:07:27 EDT 2016
    emaste@feynman:/tank/emaste/obj/tank/emaste/src/freebsd-xlld/sys/GENERIC amd64
FreeBSD clang version 3.8.0 (tags/RELEASE_380/final 262564) (based on LLVM 3.8.0)
WARNING: WITNESS option enabled, expect reduced performance.
VT(efifb): resolution 800x600
CPU: QEMU Virtual CPU version 2.5+ (3430.58-MHz K8-class CPU)
  Origin="AuthenticAMD"  Id=0x663  Family=0x6  Model=0x6  Stepping=3
  Features=0x783fbfd<FPU,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE,SSE2>
  Features2=0x80002001<SSE3,CX16,HV>
  AMD Features=0x20100800<SYSCALL,NX,LM>
  AMD Features2=0x5<LAHF,SVM>
  SVM: NAsids=16
real memory  = 268238848 (255 MB)
avail memory = 213946368 (204 MB)
Event timer "LAPIC" quality 400
ACPI APIC Table: <OVMF   OVMFEDK2>
panic: vm_wait in early boot
cpuid = 0
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffffff81e01a40
vpanic() at vpanic+0x182/frame 0xffffffff81e01ac0
panic() at panic+0x43/frame 0xffffffff81e01b20
vm_wait() at vm_wait+0xd6/frame 0xffffffff81e01b40
kmem_alloc_contig() at kmem_alloc_contig+0x1bd/frame 0xffffffff81e01c00
contigmalloc() at contigmalloc+0x33/frame 0xffffffff81e01c40
x86bios_modevent() at x86bios_modevent+0x21a/frame 0xffffffff81e01c60
module_register_init() at module_register_init+0xb0/frame 0xffffffff81e01c90
mi_startup() at mi_startup+0x118/frame 0xffffffff81e01cb0
btext() at btext+0x2c
KDB: enter: panic
[ thread pid 0 tid 0 ]
Stopped at      kdb_enter+0x3b: movq    $0,kdb_why
db>

[kib]

Use freebsd cdefs.h name.

[emaste]

FWIW this is what prompted the contigmalloc failure:

real memory  = 268238848 (255 MB)
Physical memory chunk(s):
0x0000000000001000 - 0x0000000000000fff, 0 bytes (0 pages)
0x0000000001e40000 - 0x000000000e776fff, 210989056 bytes (51511 pages)
0x000000000ee4e000 - 0x000000000fecdfff, 17301504 bytes (4224 pages)
0x000000000ff32000 - 0x000000000ffb7fff, 548864 bytes (134 pages)
avail memory = 213946368 (204 MB)

[markj]

Shouldn't the policy be determined by the contigmalloc() caller? Not all contigmalloc failures during boot are fatal, see D7417 for instance.

[kib]

In D8421#175264, @markj wrote:

Shouldn't the policy be determined by the contigmalloc() caller? Not all contigmalloc failures during boot are fatal, see D7417 for instance.

Yes, in the backtrace I posted, the reasonable action by the caller is to use M_NOWAIT if in early boot stage. Note that cold state != pagedaemon active state, there are fine differences. Even pageproc != NULL is not ideal, but is IMO better approximation than cold.

That said, D7417 is really complimentary to this change. D7417 tries to auto-correct the callers in a way I formulated in the paragraph above, while my change provides just a better message for the failure mode where either caller is not fixed or auto-correction was not applied. I.e. right now the system panics anyway if any (vm_page_alloc_contig or vm_page_alloc) allocation failed from the waitable caller, but with a cryptic message about thread not runnable, which requires somebody else than the driver author, to interpret.

[markj]

In D8421#175283, @kib wrote:

D7417 tries to auto-correct the callers in a way I formulated in the paragraph above, while my change provides just a better message for the failure mode where either caller is not fixed or auto-correction was not applied. I.e. right now the system panics anyway if any (vm_page_alloc_contig or vm_page_alloc) allocation failed from the waitable caller, but with a cryptic message about thread not runnable, which requires somebody else than the driver author, to interpret.

Indeed, this change makes sense to me as a safety belt.