I think it's uvm_purge(), as far as I can see it happens when building
rust with cvs up -D2025/06/04 in /sys, not with -D2025/06/03. Maybe I
missed lang/rust when testing the diff.
This is with additional MP_LOCKDEBUG support for mutexes, and
__mp_lock_spinout = 50L * INT_MAX.
Suggested by claudio: tr /t 0t269515 fails.
WITNESS doesn't flag an obvious lock ordering issue. I'm not even
sure there is one. It also happen with CPU_MAX_BUSY_CYCLES == 64.
Maybe we're still hammering too much the locks? Input and ideas to
test welcome. Right now I'm running with just uvm_purge() reverted.
mtx_enter: 0xffffff80012c1660 lock spun out
Stopped at mtx_enter+0x134: ldr x26, [x25,#2712]
ddb{9}> tr
db_enter() at mtx_enter+0x130
mtx_enter() at uvm_pmr_getpages+0x16c
uvm_pmr_getpages() at uvm_pmr_cache_alloc+0x74
uvm_pmr_cache_alloc() at uvm_pmr_cache_get+0x114
uvm_pmr_cache_get() at uvm_pagealloc+0xc4
uvm_pagealloc() at uvmfault_promote+0xac
uvmfault_promote() at uvm_fault_lower+0x2e4
uvm_fault_lower() at uvm_fault+0x158
uvm_fault() at udata_abort+0x128
udata_abort() at do_el0_sync+0x100
do_el0_sync() at handle_el0_sync+0x70
handle_el0_sync() at __ALIGN_SIZE+0x6154444
--- trap ---
end of kernel
ddb{9}> ps /o
TID PID UID PRFLAGS PFLAGS CPU COMMAND
439247 54947 55 0x3 0 7 c++
*151355 72169 55 0x3 0 9 c++
391653 25519 55 0x3 0 8 c++
269515 26465 55 0x3 0 4 c++
264732 5469 55 0x3 0 6 c++
473294 43623 55 0x2000003 0x4000000 1 rustc
388499 43623 55 0x2000003 0x4000000 5 rustc
132024 43623 55 0x2000003 0x4000000 3 rustc
294256 43623 55 0x2000003 0x4000000 0 rustc
ddb{9}> show all locks
CPU 4:
exclusive mutex &uvm.fpageqlock r = 0 (0xffffff80012c1670)
CPU 2:
exclusive mutex &sched_lock r = 0 (0xffffff80012c2348)
Process 54947 (c++) thread 0xffffff825a1cf9c0 (439247)
exclusive rwlock amaplk r = 0 (0xffffff8113992b68)
shared rwlock vmmaplk r = 0 (0xffffff81112ffe78)
Process 72169 (c++) thread 0xffffff825a1cf738 (151355)
exclusive rwlock amaplk r = 0 (0xffffff8113992418)
shared rwlock vmmaplk r = 0 (0xffffff81112ff518)
Process 25519 (c++) thread 0xffffff825a1d14a0 (391653)
exclusive rwlock amaplk r = 0 (0xffffff80541125c0)
shared rwlock vmmaplk r = 0 (0xffffff80547f5e60)
Process 26465 (c++) thread 0xffffff825a1d1218 (269515)
exclusive rwlock amaplk r = 0 (0xffffff81120f34e0)
Process 5469 (c++) thread 0xffffff825a1cefa0 (264732)
exclusive rwlock amaplk r = 0 (0xffffff811645d3d8)
shared rwlock vmmaplk r = 0 (0xffffff81112ff338)
Process 43623 (rustc) thread 0xffffff825a1d0f90 (166842)
exclusive rwlock sysctllk r = 0 (0xffffff8001231b60)
Process 43623 (rustc) thread 0xffffff825a1d0060 (294256)
exclusive rwlock amaplk r = 0 (0xffffff811645d858)
shared rwlock vmmaplk r = 0 (0xffffff81112ff8d8)
ddb{9}> sh struct mutex 0xffffff80012c1660
struct mutex at 0xffffff80012c1660 (56 bytes) {mtx_owner = (void *)0xffffff8055
63d000, mtx_wantipl = 8, mtx_oldipl = 0, mtx_lock_obj = {lo_type = (const lock_
type *)0x0, lo_name = (const unsigned char *)0xffffff8000e3ae71, lo_witness = (
struct witness *)0xffffff80043eb280, lo_relative = (struct lock_object *)0x0, l
o_flags = 16973824}}
ddb{9}> x/s 0xffffff8000e3ae71
$d+0x122: &uvm.fpageqlock
ddb{9}>
--
jca
