Trace buffer size not checked if fits in memory

[Adek336]

Hybrid build r28827 with 200 MiB trace buffer run under QEMU with 200 MiB hangs after showing the boot screen; none of the boot icons are alight. F12 doesn't open the KDL.

qemu -s and gdb provided the following backtrace

#0  0x800556ba in spin ()
#1  0x800b88c8 in arch_debug_blue_screen_getchar ()
#2  0x80057ee1 in blue_screen_getchar ()
#3  0x80059905 in read_line ()
#4  0x8005a4d4 in kernel_debugger ()
#5  0x8005a67b in panic ()
#6  0x800364b5 in ConditionVariableEntry::Wait ()
#7  0x800366ed in ConditionVariable::Wait ()
#8  0x8003e2f8 in low_resource ()
#9  0x800a94fe in vm_try_reserve_memory ()
#10 0x800abafd in vm_create_anonymous_area ()
#11 0x800ac204 in create_area ()
#12 0x8005e6f2 in tracing_init ()
#13 0x80059c92 in debug_init_post_vm ()
#14 0x8003ef3f in _start ()

and the following panic message

(gdb) up
#6  0x8005a67b in panic ()
(gdb) info frame
Stack level 6, frame at 0x80204d48:
 eip = 0x8005a67b in panic; saved eip 0x800364b5
 called by frame at 0x80204d88, caller of frame at 0x80204c98
 Arglist at 0x80204d40, args:
 Locals at 0x80204d40, Previous frame's sp is 0x80204d48
 Saved registers:
  ebx at 0x80204d3c, ebp at 0x80204d40, eip at 0x80204d44
(gdb) x/12xw 0x80204d40
0x80204d40:     0x80204d80      0x800364b5      0x800f201c      0x80204dc0
0x80204d50:     0x80109788      0x00200092      0x00bfe883      0x00000000
0x80204d60:     0x80204d90      0x80036307      0x801064b8      0x00000000
(gdb) x/s 0x800f201c
0x800f201c:      "ConditionVariableEntry::Wait() called with interrupts disabled, entry: %p, variable: %p"

Entering "reb<cr>" reboots the machine.

[Adek336]

With qemu -serial stdio:

...
Load kernel...
video mode: 1024x768x24
smp: found 1 cpu
smp: apic_phys = 0xfee00000
smp: ioapic_phys = 0xfec00000
smp: apic = 0x8069d000
smp: ioapic = 0x8069e000
APIC ticks/sec = 998405238
kernel entry at 8003edfa
Welcome to kernel debugger output!
Haiku revision: 28827
CPU 0: type 0 family 6 extended_family 0 model 3 extended_model 0 stepping 3, string 'GenuineIntel'
CPU 0: features: fpu de pse tsc msr pae mce cx8 apic sep pge cmov pat mmx fxsr sse sse2 sse3
heap_add_area: area -1 added to small heap 0x80ea4000 - usable range 0x80eab000 - 0x812a4000
heap_add_area: area -1 added to medium heap 0x812a4000 - usable range 0x812a5000 - 0x8150a000
heap_add_area: area -1 added to large heap 0x8150a666 - usable range 0x8150b000 - 0x816a4000
slab: init base 0x816a4000 + 0x2000
vm_mark_page_range_inuse: page 0x9f in non-free state 7!
PANIC: ConditionVariableEntry::Wait() called with interrupts disabled, entry: 0x80204dc0, variable: 0x80109788
Welcome to Kernel Debugging Land...
Thread 0 "" running on CPU 0
kdebug> bt
Unknown command "bt". Enter "help" to get a list of all supported commands.

[Adek336]

Obviously 200 MiB is more than the default 128 MiB RAM size in QEMU. qemu -m 400 makes Haiku work just fine!

Too bad the kernel debugger isn't shown on screen when Haiku panics at such an early stage (#3238). If it did show up, it would be reasonable to panic with a message "Trace buffer too large".

[Adek336]

And resizing the trace buffer or at least disabling tracing.