PR/59037 CVS commit: [netbsd-10] src/sys

["Martin Husemann" <martin%netbsd.org@localhost>]

The following reply was made to PR kern/59037; it has been noted by GNATS.

From: "Martin Husemann" <martin%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/59037 CVS commit: [netbsd-10] src/sys
Date: Fri, 9 May 2025 12:59:59 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Fri May  9 12:59:59 UTC 2025
 
 Modified Files:
 	src/sys/kern [netbsd-10]: kern_exec.c
 	src/sys/uvm [netbsd-10]: uvm_extern.h uvm_map.c
 
 Log Message:
 Pull up following revision(s) (requested by riastradh in ticket #1109):
 
 	sys/uvm/uvm_extern.h: revision 1.234
 	sys/kern/kern_exec.c: revision 1.528
 	sys/uvm/uvm_map.c: revision 1.427
 
 posix_spawn(2): Allocate a new vmspace at process creation time.
 
 This allocates a new vmspace for the process at the time the new
 process is created, rather than sharing some other vmspace temporarily.
 
 This eliminates any risk of anything bad happening due to temporary
 sharing, since there isn't any sharing.
 
 Resolves a race to where:
 1. we set up the child to share proc0.p_vmspace at first,
 2. another process tries to read the new child's psstrings via
    kern.proc_args.<childpid>.argv or similar with the child's
    p_reflock held and gets stuck in a uvm fault loop because
    proc0.p_vmspace doesn't have the child's psstrings address
    (inherited from the parent) mapped,
 3. the child is waiting for p_reflock before it can replace its
    p_vmspace or psstrings.
 
 By allocating the vmspace up front, with no mappings in it, we avoid
 exposing the child in this scenario.  Minor possible downside is that
 sysctl kern.proc_args.<childpid>.argv might spuriously fail with
 EFAULT during this time (rather than fail with EBUSY as it does if
 p_reflock is held concurrently) but that's not a particularly big
 deal.
 
 Patch and first paragraph of commit message written by chs@; minor
 tweaks to comments -- and any mistakes in the analysis -- by me.
 
 PR kern/59037: deadlock in posix_spawn
 PR kern/59175: posix_spawn hang, hanging other process too
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.518.4.1 -r1.518.4.2 src/sys/kern/kern_exec.c
 cvs rdiff -u -r1.232 -r1.232.12.1 src/sys/uvm/uvm_extern.h
 cvs rdiff -u -r1.403.2.3 -r1.403.2.4 src/sys/uvm/uvm_map.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.