Re: kern/56764: panic assertion "uvmexp.swpgonly > 0"

["Thomas Klausner via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/56764; it has been noted by GNATS.

From: Thomas Klausner <wiz%NetBSD.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: Chuck Silvers <chuq%chuq.com@localhost>
Subject: Re: kern/56764: panic assertion "uvmexp.swpgonly > 0"
Date: Mon, 25 Aug 2025 13:55:38 +0200

 I haven't seen this particular panic yet, but I have problems with
 this counter since at least 2017.
 
 My latest one was
 
 panic: kernel diagnostic assertion "uvmexp.swpgonly < uvmexp.swpginuse" failed: file "/usr/src/sys/uvm/uvm_pdaemon.c", line 795
 
 The backtrace is
 (gdb) bt
 #0  0xffffffff80239b85 in cpu_reboot (howto=howto@entry=260, bootstr=bootstr@entry=0x0) at /usr/src/sys/arch/amd64/amd64/machdep.c:709
 #1  0xffffffff80de5a95 in kern_reboot (howto=howto@entry=260, bootstr=bootstr@entry=0x0) at /usr/src/sys/kern/kern_reboot.c:91
 #2  0xffffffff80e2ba63 in vpanic (fmt=0xffffffff81427c00 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ", ap=ap@entry=0xffffc1a47baa2e98) at /usr/src/sys/kern/subr_prf.c:288
 #3  0xffffffff80ffb6fe in kern_assert (fmt=fmt@entry=0xffffffff81427c00 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ") at /usr/src/sys/lib/libkern/kern_assert.c:51
 #4  0xffffffff80d9532c in uvmpd_scan_queue () at /usr/src/sys/uvm/uvm_pdaemon.c:795
 #5  uvmpd_scan () at /usr/src/sys/uvm/uvm_pdaemon.c:917
 #6  uvm_pageout (arg=<optimized out>) at /usr/src/sys/uvm/uvm_pdaemon.c:318
 #7  0xffffffff80210327 in lwp_trampoline ()
 #8  0x0000000000000000 in ?? ()
 
 Chuck Silvers took a number of looks at this over the years, and his
 best guess is that the counters are not maintained correctly, but we
 haven't found the root cause of this.
  Thomas