Re: kern/58760: running fdisk(8) on a vnd(4) backed by NFS crashes the kernel

["Michael van Elst via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/58760; it has been noted by GNATS.

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/58760: running fdisk(8) on a vnd(4) backed by NFS crashes the kernel
Date: Sat, 19 Oct 2024 22:04:50 -0000 (UTC)

 martin%NetBSD.org@localhost writes:
 
 >[ 685.0814275] panic: nfs physio/async
 >[ 685.0814275] cpu0: Begin traceback...
 >[ 685.0814275] 0xd4d2fe74: netbsd:db_panic+0x14
 >[ 685.0814275] 0xd4d2fe94: netbsd:vpanic+0x14c
 >[ 685.0814275] 0xd4d2feac: netbsd:panic+0x24
 >[ 685.0814275] 0xd4d2fed4: netbsd:nfs_strategy+0x60
 >[ 685.0814275] 0xd4d2fefc: netbsd:VOP_STRATEGY+0x68
 >[ 685.0814275] 0xd4d2ffac: netbsd:vndthread+0x7d0
 
 
 fdisk uses physio, so the original buffer is marked B_PHYS.
 vnd creates a nestiobuf which inherits B_PHYS but is also
 marked with B_ASYNC as it doesn't finish the I/O request
 itself.
 
 NFS panics if B_PHYS and B_ASYNC are set.
 
 nfs_vnops.c 1.32 (merge with 4.4lite2) introduced the panic
 for B_PHYS alone, nfs_vnops.c 1.33 refined this to require
 B_ASYNC as well.