https://github.com/torvalds/linux
Revision 0c36b390a546055b6815d4b93a2c9fed4d980ffb authored by Sebastian Ott on 04 June 2014, 13:58:24 UTC, committed by Tejun Heo on 04 June 2014, 16:12:29 UTC
The percpu-refcount infrastructure uses the underscore variants of
this_cpu_ops in order to modify percpu reference counters.
(e.g. __this_cpu_inc()).

However the underscore variants do not atomically update the percpu
variable, instead they may be implemented using read-modify-write
semantics (more than one instruction).  Therefore it is only safe to
use the underscore variant if the context is always the same (process,
softirq, or hardirq). Otherwise it is possible to lose updates.

This problem is something that Sebastian has seen within the aio
subsystem which uses percpu refcounters both in process and softirq
context leading to reference counts that never dropped to zeroes; even
though the number of "get" and "put" calls matched.

Fix this by using the non-underscore this_cpu_ops variant which
provides correct per cpu atomic semantics and fixes the corrupted
reference counts.

Cc: Kent Overstreet <kmo@daterainc.com>
Cc: <stable@vger.kernel.org> # v3.11+
Reported-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
References: http://lkml.kernel.org/g/alpine.LFD.2.11.1406041540520.21183@denkbrett
1 parent 5a838c3
Raw File
Tip revision: 0c36b390a546055b6815d4b93a2c9fed4d980ffb authored by Sebastian Ott on 04 June 2014, 13:58:24 UTC
percpu-refcount: fix usage of this_cpu_ops
Tip revision: 0c36b39
coccicheck
#!/bin/bash

#
# This script requires at least spatch
# version 1.0.0-rc11.
#

SPATCH="`which ${SPATCH:=spatch}`"

trap kill_running SIGTERM SIGINT
declare -a SPATCH_PID

# The verbosity may be set by the environmental parameter V=
# as for example with 'make V=1 coccicheck'

if [ -n "$V" -a "$V" != "0" ]; then
	VERBOSE="$V"
else
	VERBOSE=0
fi

if [ -z "$J" ]; then
	NPROC=$(getconf _NPROCESSORS_ONLN)
else
	NPROC="$J"
fi

FLAGS="$SPFLAGS --very-quiet"

# spatch only allows include directories with the syntax "-I include"
# while gcc also allows "-Iinclude" and "-include include"
COCCIINCLUDE=${LINUXINCLUDE//-I/-I }
COCCIINCLUDE=${COCCIINCLUDE//-include/-I}

if [ "$C" = "1" -o "$C" = "2" ]; then
    ONLINE=1

    # Take only the last argument, which is the C file to test
    shift $(( $# - 1 ))
    OPTIONS="$COCCIINCLUDE $1"
else
    ONLINE=0
    if [ "$KBUILD_EXTMOD" = "" ] ; then
        OPTIONS="--dir $srctree $COCCIINCLUDE"
    else
        OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
    fi
fi

if [ "$KBUILD_EXTMOD" != "" ] ; then
    OPTIONS="--patch $srctree $OPTIONS"
fi

if [ ! -x "$SPATCH" ]; then
    echo 'spatch is part of the Coccinelle project and is available at http://coccinelle.lip6.fr/'
    exit 1
fi

if [ "$MODE" = "" ] ; then
    if [ "$ONLINE" = "0" ] ; then
	echo 'You have not explicitly specified the mode to use. Using default "report" mode.'
	echo 'Available modes are the following: patch, report, context, org'
	echo 'You can specify the mode with "make coccicheck MODE=<mode>"'
	echo 'Note however that some modes are not implemented by some semantic patches.'
    fi
    MODE="report"
fi

if [ "$MODE" = "chain" ] ; then
    if [ "$ONLINE" = "0" ] ; then
	echo 'You have selected the "chain" mode.'
	echo 'All available modes will be tried (in that order): patch, report, context, org'
    fi
elif [ "$MODE" = "report" -o "$MODE" = "org" ] ; then
    FLAGS="$FLAGS --no-show-diff"
fi

if [ "$ONLINE" = "0" ] ; then
    echo ''
    echo 'Please check for false positives in the output before submitting a patch.'
    echo 'When using "patch" mode, carefully review the patch before submitting it.'
    echo ''
fi

run_cmd() {
	local i
	if [ $VERBOSE -ne 0 ] ; then
		echo "Running ($NPROC in parallel): $@"
	fi
	for i in $(seq 0 $(( NPROC - 1)) ); do
		eval "$@ --max $NPROC --index $i &"
		SPATCH_PID[$i]=$!
		if [ $VERBOSE -eq 2 ] ; then
			echo "${SPATCH_PID[$i]} running"
		fi
	done
	wait
}

kill_running() {
	for i in $(seq $(( NPROC - 1 )) ); do
		if [ $VERBOSE -eq 2 ] ; then
			echo "Killing ${SPATCH_PID[$i]}"
		fi
		kill ${SPATCH_PID[$i]} 2>/dev/null
	done
}

coccinelle () {
    COCCI="$1"

    OPT=`grep "Option" $COCCI | cut -d':' -f2`

#   The option '--parse-cocci' can be used to syntactically check the SmPL files.
#
#    $SPATCH -D $MODE $FLAGS -parse_cocci $COCCI $OPT > /dev/null

    if [ $VERBOSE -ne 0 -a $ONLINE -eq 0 ] ; then

	FILE=`echo $COCCI | sed "s|$srctree/||"`

	echo "Processing `basename $COCCI`"
	echo "with option(s) \"$OPT\""
	echo ''
	echo 'Message example to submit a patch:'

	sed -ne 's|^///||p' $COCCI

	if [ "$MODE" = "patch" ] ; then
	    echo ' The semantic patch that makes this change is available'
	elif [ "$MODE" = "report" ] ; then
	    echo ' The semantic patch that makes this report is available'
	elif [ "$MODE" = "context" ] ; then
	    echo ' The semantic patch that spots this code is available'
	elif [ "$MODE" = "org" ] ; then
	    echo ' The semantic patch that makes this Org report is available'
	else
	    echo ' The semantic patch that makes this output is available'
	fi
	echo " in $FILE."
	echo ''
	echo ' More information about semantic patching is available at'
	echo ' http://coccinelle.lip6.fr/'
	echo ''

	if [ "`sed -ne 's|^//#||p' $COCCI`" ] ; then
	    echo 'Semantic patch information:'
	    sed -ne 's|^//#||p' $COCCI
	    echo ''
	fi
    fi

    if [ "$MODE" = "chain" ] ; then
	run_cmd $SPATCH -D patch   \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS               || \
	run_cmd $SPATCH -D report  \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff || \
	run_cmd $SPATCH -D context \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS               || \
	run_cmd $SPATCH -D org     \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff || exit 1
    elif [ "$MODE" = "rep+ctxt" ] ; then
	run_cmd $SPATCH -D report  \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff && \
	run_cmd $SPATCH -D context \
		$FLAGS --cocci-file $COCCI $OPT $OPTIONS || exit 1
    else
	run_cmd $SPATCH -D $MODE   $FLAGS --cocci-file $COCCI $OPT $OPTIONS || exit 1
    fi

}

if [ "$COCCI" = "" ] ; then
    for f in `find $srctree/scripts/coccinelle/ -name '*.cocci' -type f | sort`; do
	coccinelle $f
    done
else
    coccinelle $COCCI
fi
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