oplock errors

[Nicolas Williams]

[NOTE: I don't subscribe to any of the Samba lists but follow them on
       the Samba list arvhices. It would be nice if the archives web
       sites included e-mail reference IDs so I can use then when
       "replying" to messages on these lists so that I don't break
       threading for others who do subscribe.]

I've posted about this problem before. I should probably make the damn
time and reproduce the bug (it's so easy to do it) and send
snoop/truss/sotruss/pstack output to the list. But as it is I won't be
able to do this for a few weeks.

Now, we've speculated here before that the oplock problem on Solaris has
to do with the FIN/ACK/data bugs in client TCP/IP stacks as well as in
the Solaris TCP/IP stack.  The Solaris bug ID is 4083814 and the Solaris
patch ID is 105529-04 (the current patch version is -07).

Now, I've also stated that I have a workaround. I include the script I
use in conjunction with root preexec/root postexec below. This
workaround works fine.

I've also stated the procedures needed to reproduce the bug:

 - make an SMB connection from an NT client to a Solaris Samba server
 - open some file on the Samba share with Word or some other program
   that'll use oplocks
 - yank the network from the Samba server
 - attempt to save the file you had opened
 - wait 45 seconds + a few seconds
 - restore the network
 - wait a bit

That's it. At that point there will be two smbd processes for the same
NT client on the Samba server: one is "stale", should die and holds the
oplock and is sleeping; the other is new and is waiting for the old smbd
to release the oplock.

If you want to read more about this problem or how to use the script
included below, search the list archives for posts from me. One Subject:
under which this has been discussed before is

"Stale smbd processes (was: DOS: Clients can freeze other clients smbd)"

You may want to read those as the script I include below is not the only
proposed solution. It's just the one I use.

Enjoy,

Nico
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#!/bin/ksh
#
# This script is meant to be run by Samba SMBdaemons as specified in
# per-share 'root preexec' and 'root postexec' parameters. The purpose
# of this script is to clean up stale smbds; this is accomplish by
# creating a PID file named after the given share connection parameters.
# Such pidfiles are removed when called by smbd as a result of the 'root
# postexec' parameter. Such pidfiles are created when called by smbd as
# a result of the 'root preexec'; if one already exists, then the script
# checks for a stale smbd and kills it if there is any.
#
# Examples:
# root preexec = /usr/local/samba/libexec/chkStaleSession preexec %d %I %h %S %U
# root postexec = /usr/local/samba/libexec/chkStaleSession postexec %d %I %h %S %U
#
# (c) Perot Systems Inc.
# Nicolas.Williams at wdr.com
#
##       @(#) chkStaleSession 1.3     09/02/99, WDR
#

## Globals
#
: ${SMB_LOCK_DIR:=/var/smb/locks}
: ${SMB_LOG_DIR:=/var/smb/log}

## concat - concatenate argument strings with given separator character
#
#	    $1 --> separator character
#	    $2, $3, ..., $n --> strings to concatenate
#
concat ()
{
	typeset OIFS
	OIFS="$IFS"
	IFS="$1"
	shift
	print -- "$*"
	IFS="$OIFS"
	return 0
}

## noclobber, see below
set -o noclobber

exec 2>> $SMB_LOG_DIR/staleSessions.log

SELF=${0##*/}

## Log our script name, pid and arguments
print -u2 "$SELF[$$]: $@"

OP=$1
shift

SMBPID=$1
shift

## Remaining argument strings identify an SMB share connection/mount
SHARE_ID="$(concat '-' "$@")"
PID_FILE="$SMB_LOCK_DIR/$SHARE_ID.pid"

status=fail

# This script uses /usr/proc/bin/ptree and /usr/proc/bin/pwait.
# For platforms other than Solaris you may have to modify it to use
# something else (e.g., ps can replace ptree).

case $OP in
	preexec)
		# Skip IPC$ connections
		for i in "$@"
		do
			[[ "$i" = 'IPC$' || "$i" = 'IPC$nobody' ]] && exit 0
		done

		## The 'noclobber' option comes into play here,
		## preventing the print command from being executed
		## if $PID_FILE exists. 'noclobber' is equivalent to
		## using open(2) with O_CREAT|O_EXCL.

		until ( print -- "$SMBPID" > "$PID_FILE" ) 2> /dev/null
		do
			OPID=$(cat "$PID_FILE")

			# Syntax check PID
			if [[ -z "$OPID" || "$OPID" != +([0-9]) ]]
			then
				print -u2 "$SELF[$$]: could not obtain old PID for $SHARE_ID"
				set +o noclobber
				print -- "$SMBPID" > "$PID_FILE"
				break
			fi

			# Check that process still exists and is an smbd
			/usr/proc/bin/ptree "$OPID"|grep smb > /dev/null 2>&1 || {
				rm "$PID_FILE" || status=rmfail
				continue
			}
			print -u2 "$SELF[$$]: sending SIGTERM to $OPID on behalf of $SHARE_ID"
			kill -TERM "$OPID"
			/usr/proc/bin/pwait "$OPID"
		done
		status=success
		;;
	postexec)
		# Skip IPC$ connections
		for i in "$@"
		do
			[[ "$i" = 'IPC$' || "$i" = 'IPC$nobody' ]] && exit 0
		done

		if [[ -f  "$PID_FILE" ]]
		then
			OPID=$(cat "$PID_FILE")
			if [[ "$OPID" = "$SMBPID" ]]
			then
				rm "$PID_FILE" || status=rmfail
			fi
		fi
		status=success
		;;
esac


case $status in
	success) exit 0
		;;
esac

print -u2 -- "$SELF[$$]: Error: ($1) pid file $PID_FILE has not been removed!"

exit 0

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