PR/59870 CVS commit: src/sys/kern

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

The following reply was made to PR kern/59870; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/59870 CVS commit: src/sys/kern
Date: Sat, 3 Jan 2026 23:08:16 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sat Jan  3 23:08:16 UTC 2026
 
 Modified Files:
 	src/sys/kern: kern_lock.c
 
 Log Message:
 KERNEL_LOCK(9): New dtrace probes for taking and dropping the lock.
 
 At some point, fbt::_kernel_lock:return worked to probe the `taking'
 part (judging by the message I wrote some years ago at
 https://mail-index.NetBSD.org/tech-kern/2022/10/30/msg028499.html)
 but no longer, so let's just make sure there is always a probe that
 explicitly works, on both sides:
 
 - sdt:kernel:lock:entry(nlocks) fires when we have determined we can
   take the kernel lock and we're about to increment its depth by
   nlocks.
 
 - sdt:kernel:lock:exit(nlocks) fires after we have released the kernel
   lock and already decremented its depth by nlocks.
 
 On first acquisition, or last release, of the kernel lock by a thread
 or CPU, in both probes the value of curlwp->l_blcnt or
 curcpu()->ci_biglock_count will be zero.
 
 PR kern/59870: kernel lock runtime diagnostics are difficult
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.190 -r1.191 src/sys/kern/kern_lock.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.