Revision 472e5b056f000a778abb41f1e443de58eb259783 authored by Linus Torvalds on 02 October 2020, 02:14:36 UTC, committed by Linus Torvalds on 02 October 2020, 02:14:36 UTC
The pipe splice code still used the old model of waiting for pipe IO by using a non-specific "pipe_wait()" that waited for any pipe event to happen, which depended on all pipe IO being entirely serialized by the pipe lock. So by checking the state you were waiting for, and then adding yourself to the wait queue before dropping the lock, you were guaranteed to see all the wakeups. Strictly speaking, the actual wakeups were not done under the lock, but the pipe_wait() model still worked, because since the waiter held the lock when checking whether it should sleep, it would always see the current state, and the wakeup was always done after updating the state. However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing") split the single wait-queue into two, and in the process also made the "wait for event" code wait for _two_ wait queues, and that then showed a race with the wakers that were not serialized by the pipe lock. It's only splice that used that "pipe_wait()" model, so the problem wasn't obvious, but Josef Bacik reports: "I hit a hang with fstest btrfs/187, which does a btrfs send into /dev/null. This works by creating a pipe, the write side is given to the kernel to write into, and the read side is handed to a thread that splices into a file, in this case /dev/null. The box that was hung had the write side stuck here [pipe_write] and the read side stuck here [splice_from_pipe_next -> pipe_wait]. [ more details about pipe_wait() scenario ] The problem is we're doing the prepare_to_wait, which sets our state each time, however we can be woken up either with reads or writes. In the case above we race with the WRITER waking us up, and re-set our state to INTERRUPTIBLE, and thus never break out of schedule" Josef had a patch that avoided the issue in pipe_wait() by just making it set the state only once, but the deeper problem is that pipe_wait() depends on a level of synchonization by the pipe mutex that it really shouldn't. And the whole "wait for any pipe state change" model really isn't very good to begin with. So rather than trying to work around things in pipe_wait(), remove that legacy model of "wait for arbitrary pipe event" entirely, and actually create functions that wait for the pipe actually being readable or writable, and can do so without depending on the pipe lock serializing everything. Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing") Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/ Reported-by: Josef Bacik <josef@toxicpanda.com> Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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patch-kernel
#! /bin/sh
# SPDX-License-Identifier: GPL-2.0
# Script to apply kernel patches.
# usage: patch-kernel [ sourcedir [ patchdir [ stopversion ] [ -acxx ] ] ]
# The source directory defaults to /usr/src/linux, and the patch
# directory defaults to the current directory.
# e.g.
# scripts/patch-kernel . ..
# Update the kernel tree in the current directory using patches in the
# directory above to the latest Linus kernel
# scripts/patch-kernel . .. -ac
# Get the latest Linux kernel and patch it with the latest ac patch
# scripts/patch-kernel . .. 2.4.9
# Gets standard kernel 2.4.9
# scripts/patch-kernel . .. 2.4.9 -ac
# Gets 2.4.9 with latest ac patches
# scripts/patch-kernel . .. 2.4.9 -ac11
# Gets 2.4.9 with ac patch ac11
# Note: It uses the patches relative to the Linus kernels, not the
# ac to ac relative patches
#
# It determines the current kernel version from the top-level Makefile.
# It then looks for patches for the next sublevel in the patch directory.
# This is applied using "patch -p1 -s" from within the kernel directory.
# A check is then made for "*.rej" files to see if the patch was
# successful. If it is, then all of the "*.orig" files are removed.
#
# Nick Holloway <Nick.Holloway@alfie.demon.co.uk>, 2nd January 1995.
#
# Added support for handling multiple types of compression. What includes
# gzip, bzip, bzip2, zip, compress, and plaintext.
#
# Adam Sulmicki <adam@cfar.umd.edu>, 1st January 1997.
#
# Added ability to stop at a given version number
# Put the full version number (i.e. 2.3.31) as the last parameter
# Dave Gilbert <linux@treblig.org>, 11th December 1999.
# Fixed previous patch so that if we are already at the correct version
# not to patch up.
#
# Added -ac option, use -ac or -ac9 (say) to stop at a particular version
# Dave Gilbert <linux@treblig.org>, 29th September 2001.
#
# Add support for (use of) EXTRAVERSION (to support 2.6.8.x, e.g.);
# update usage message;
# fix some whitespace damage;
# be smarter about stopping when current version is larger than requested;
# Randy Dunlap <rdunlap@xenotime.net>, 2004-AUG-18.
#
# Add better support for (non-incremental) 2.6.x.y patches;
# If an ending version number if not specified, the script automatically
# increments the SUBLEVEL (x in 2.6.x.y) until no more patch files are found;
# however, EXTRAVERSION (y in 2.6.x.y) is never automatically incremented
# but must be specified fully.
#
# patch-kernel does not normally support reverse patching, but does so when
# applying EXTRAVERSION (x.y) patches, so that moving from 2.6.11.y to 2.6.11.z
# is easy and handled by the script (reverse 2.6.11.y and apply 2.6.11.z).
# Randy Dunlap <rdunlap@xenotime.net>, 2005-APR-08.
PNAME=patch-kernel
# Set directories from arguments, or use defaults.
sourcedir=${1-/usr/src/linux}
patchdir=${2-.}
stopvers=${3-default}
if [ "$1" = -h -o "$1" = --help -o ! -r "$sourcedir/Makefile" ]; then
cat << USAGE
usage: $PNAME [-h] [ sourcedir [ patchdir [ stopversion ] [ -acxx ] ] ]
source directory defaults to /usr/src/linux,
patch directory defaults to the current directory,
stopversion defaults to <all in patchdir>.
USAGE
exit 1
fi
# See if we have any -ac options
for PARM in $*
do
case $PARM in
-ac*)
gotac=$PARM;
esac;
done
# ---------------------------------------------------------------------------
# arg1 is filename
noFile () {
echo "cannot find patch file: ${patch}"
exit 1
}
# ---------------------------------------------------------------------------
backwards () {
echo "$PNAME does not support reverse patching"
exit 1
}
# ---------------------------------------------------------------------------
# Find a file, first parameter is basename of file
# it tries many compression mechanisms and sets variables to say how to get it
findFile () {
filebase=$1;
if [ -r ${filebase}.gz ]; then
ext=".gz"
name="gzip"
uncomp="gunzip -dc"
elif [ -r ${filebase}.bz ]; then
ext=".bz"
name="bzip"
uncomp="bunzip -dc"
elif [ -r ${filebase}.bz2 ]; then
ext=".bz2"
name="bzip2"
uncomp="bunzip2 -dc"
elif [ -r ${filebase}.xz ]; then
ext=".xz"
name="xz"
uncomp="xz -dc"
elif [ -r ${filebase}.zip ]; then
ext=".zip"
name="zip"
uncomp="unzip -d"
elif [ -r ${filebase}.Z ]; then
ext=".Z"
name="uncompress"
uncomp="uncompress -c"
elif [ -r ${filebase} ]; then
ext=""
name="plaintext"
uncomp="cat"
else
return 1;
fi
return 0;
}
# ---------------------------------------------------------------------------
# Apply a patch and check it goes in cleanly
# First param is patch name (e.g. patch-2.4.9-ac5) - without path or extension
applyPatch () {
echo -n "Applying $1 (${name})... "
if $uncomp ${patchdir}/$1${ext} | patch -p1 -s -N -E -d $sourcedir
then
echo "done."
else
echo "failed. Clean up yourself."
return 1;
fi
if [ "`find $sourcedir/ '(' -name '*.rej' -o -name '.*.rej' ')' -print`" ]
then
echo "Aborting. Reject files found."
return 1;
fi
# Remove backup files
find $sourcedir/ '(' -name '*.orig' -o -name '.*.orig' ')' -exec rm -f {} \;
return 0;
}
# ---------------------------------------------------------------------------
# arg1 is patch filename
reversePatch () {
echo -n "Reversing $1 (${name}) ... "
if $uncomp ${patchdir}/"$1"${ext} | patch -p1 -Rs -N -E -d $sourcedir
then
echo "done."
else
echo "failed. Clean it up."
exit 1
fi
if [ "`find $sourcedir/ '(' -name '*.rej' -o -name '.*.rej' ')' -print`" ]
then
echo "Aborting. Reject files found."
return 1
fi
# Remove backup files
find $sourcedir/ '(' -name '*.orig' -o -name '.*.orig' ')' -exec rm -f {} \;
return 0
}
# set current VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
# force $TMPFILEs below to be in local directory: a slash character prevents
# the dot command from using the search path.
TMPFILE=`mktemp ./.tmpver.XXXXXX` || { echo "cannot make temp file" ; exit 1; }
grep -E "^(VERSION|PATCHLEVEL|SUBLEVEL|EXTRAVERSION)" $sourcedir/Makefile > $TMPFILE
tr -d [:blank:] < $TMPFILE > $TMPFILE.1
. $TMPFILE.1
rm -f $TMPFILE*
if [ -z "$VERSION" -o -z "$PATCHLEVEL" -o -z "$SUBLEVEL" ]
then
echo "unable to determine current kernel version" >&2
exit 1
fi
NAME=`grep ^NAME $sourcedir/Makefile`
NAME=${NAME##*=}
echo "Current kernel version is $VERSION.$PATCHLEVEL.$SUBLEVEL${EXTRAVERSION} ($NAME)"
# strip EXTRAVERSION to just a number (drop leading '.' and trailing additions)
EXTRAVER=
if [ x$EXTRAVERSION != "x" ]
then
EXTRAVER=${EXTRAVERSION#.}
EXTRAVER=${EXTRAVER%%[[:punct:]]*}
#echo "$PNAME: changing EXTRAVERSION from $EXTRAVERSION to $EXTRAVER"
fi
#echo "stopvers=$stopvers"
if [ $stopvers != "default" ]; then
STOPSUBLEVEL=`echo $stopvers | cut -d. -f3`
STOPEXTRA=`echo $stopvers | cut -d. -f4`
STOPFULLVERSION=${stopvers%%.$STOPEXTRA}
#echo "#___STOPSUBLEVEL=/$STOPSUBLEVEL/, STOPEXTRA=/$STOPEXTRA/"
else
STOPSUBLEVEL=9999
STOPEXTRA=9999
fi
# This all assumes a 2.6.x[.y] kernel tree.
# Don't allow backwards/reverse patching.
if [ $STOPSUBLEVEL -lt $SUBLEVEL ]; then
backwards
fi
if [ x$EXTRAVER != "x" ]; then
CURRENTFULLVERSION="$VERSION.$PATCHLEVEL.$SUBLEVEL.$EXTRAVER"
else
CURRENTFULLVERSION="$VERSION.$PATCHLEVEL.$SUBLEVEL"
fi
if [ x$EXTRAVER != "x" ]; then
echo "backing up to: $VERSION.$PATCHLEVEL.$SUBLEVEL"
patch="patch-${CURRENTFULLVERSION}"
findFile $patchdir/${patch} || noFile ${patch}
reversePatch ${patch} || exit 1
fi
# now current is 2.6.x, with no EXTRA applied,
# so update to target SUBLEVEL (2.6.SUBLEVEL)
# and then to target EXTRAVER (2.6.SUB.EXTRAVER) if requested.
# If not ending sublevel is specified, it is incremented until
# no further sublevels are found.
if [ $STOPSUBLEVEL -gt $SUBLEVEL ]; then
while : # incrementing SUBLEVEL (s in v.p.s)
do
CURRENTFULLVERSION="$VERSION.$PATCHLEVEL.$SUBLEVEL"
EXTRAVER=
if [ x$STOPFULLVERSION = x$CURRENTFULLVERSION ]; then
echo "Stopping at $CURRENTFULLVERSION base as requested."
break
fi
SUBLEVEL=$(($SUBLEVEL + 1))
FULLVERSION="$VERSION.$PATCHLEVEL.$SUBLEVEL"
#echo "#___ trying $FULLVERSION ___"
if [ $(($SUBLEVEL)) -gt $(($STOPSUBLEVEL)) ]; then
echo "Stopping since sublevel ($SUBLEVEL) is beyond stop-sublevel ($STOPSUBLEVEL)"
exit 1
fi
patch=patch-$FULLVERSION
# See if the file exists and find extension
findFile $patchdir/${patch} || noFile ${patch}
# Apply the patch and check all is OK
applyPatch $patch || break
done
#echo "#___sublevel all done"
fi
# There is no incremental searching for extraversion...
if [ "$STOPEXTRA" != "" ]; then
while : # just to allow break
do
# apply STOPEXTRA directly (not incrementally) (x in v.p.s.x)
FULLVERSION="$VERSION.$PATCHLEVEL.$SUBLEVEL.$STOPEXTRA"
#echo "#... trying $FULLVERSION ..."
patch=patch-$FULLVERSION
# See if the file exists and find extension
findFile $patchdir/${patch} || noFile ${patch}
# Apply the patch and check all is OK
applyPatch $patch || break
#echo "#___extraver all done"
break
done
fi
if [ x$gotac != x ]; then
# Out great user wants the -ac patches
# They could have done -ac (get latest) or -acxx where xx=version they want
if [ $gotac = "-ac" ]; then
# They want the latest version
HIGHESTPATCH=0
for PATCHNAMES in $patchdir/patch-${CURRENTFULLVERSION}-ac*\.*
do
ACVALUE=`echo $PATCHNAMES | sed -e 's/^.*patch-[0-9.]*-ac\([0-9]*\).*/\1/'`
# Check it is actually a recognised patch type
findFile $patchdir/patch-${CURRENTFULLVERSION}-ac${ACVALUE} || break
if [ $ACVALUE -gt $HIGHESTPATCH ]; then
HIGHESTPATCH=$ACVALUE
fi
done
if [ $HIGHESTPATCH -ne 0 ]; then
findFile $patchdir/patch-${CURRENTFULLVERSION}-ac${HIGHESTPATCH} || break
applyPatch patch-${CURRENTFULLVERSION}-ac${HIGHESTPATCH}
else
echo "No -ac patches found"
fi
else
# They want an exact version
findFile $patchdir/patch-${CURRENTFULLVERSION}${gotac} || {
echo "Sorry, I couldn't find the $gotac patch for $CURRENTFULLVERSION. Hohum."
exit 1
}
applyPatch patch-${CURRENTFULLVERSION}${gotac}
fi
fi
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