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Merge branch 'main' of https://github.com/PacktPublishing/Linux-Kernel-Programming_2E

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Kaiwan N Billimoria
2023-11-20 10:24:58 +05:30
parent deed1ca576 a5f8b3ae9f
commit cc16828119
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297
ch13/3_lockfree/thrdshowall_rcu/Makefile Normal file
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# ch5/lkm_template/Makefile
# ***************************************************************
# This program is part of the source code released for the book
# "Linux Kernel Programming" 2E
# (c) Author: Kaiwan N Billimoria
# Publisher: Packt
# GitHub repository:
# https://github.com/PacktPublishing/Linux-Kernel-Programming_2E
#
# From: Ch 5 : Writing Your First Kernel Module LKMs, Part 2
# ***************************************************************
# Brief Description:
# A 'better' Makefile template for Linux LKMs (Loadable Kernel Modules); besides
# the 'usual' targets (the build, install and clean), we incorporate targets to
# do useful (and indeed required) stuff like:
# - adhering to kernel coding style (indent+checkpatch)
# - several static analysis targets (via sparse, gcc, flawfinder, cppcheck)
# - two _dummy_ dynamic analysis targets (KASAN, LOCKDEP); just to remind you!
# - a packaging (.tar.xz) target and
# - a help target.
#
# To get started, just type:
# make help
#
# For details, please refer the book, Ch 5, section
# 'A "better" Makefile template for your kernel modules'.
#
# AUTHOR : Kaiwan N Billimoria
# DESCRIPTION : A simple kernel module 'better' Makefile template
# LICENSE : Dual MIT/GPL
# VERSION : 0.2
#------------------------------------------------------------------
# IMPORTANT : Set FNAME_C to the kernel module name source filename (without .c).
# This enables you to use this Makefile as a template; just update this variable!
# As well, the MYDEBUG variable (see it below) can be set to 'y' or 'n' (no being
# the default)
FNAME_C := thrd_showall_rcu
ifeq ($(FNAME_C),)
$(error ERROR: you Must set the FNAME_C variable in the Makefile)
endif
#------------------------------------------------------------------
#--- To support cross-compiling for kernel modules
# For architecture (cpu) 'arch', invoke make as:
# make ARCH=<arch> CROSS_COMPILE=<cross-compiler-prefix>
# F.e. to cross-compile for the AArch64:
# make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
#
# Alternately:
# export ARCH=<arch>
# export CROSS_COMPILE=<cross-compiler-prefix>
# make
#
# The KDIR var is set to a sample path below; you're expected to update it on
# your box to the appropriate path to the kernel source tree for that arch.
ifeq ($(ARCH),arm)
# *UPDATE* 'KDIR' below to point to the ARM Linux kernel source tree on your box
KDIR ?= ~/arm_prj/kernel/linux
else ifeq ($(ARCH),arm64)
# *UPDATE* 'KDIR' below to point to the ARM64 (Aarch64) Linux kernel source
# tree on your box
KDIR ?= ~/arm64_prj/kernel/linux-5.10.60
else ifeq ($(ARCH),powerpc)
# *UPDATE* 'KDIR' below to point to the PPC64 Linux kernel source tree on your box
KDIR ?= ~/ppc_prj/kernel/linux-5.4
else
# 'KDIR' is the Linux 'kernel headers' package on your host system; this is
# usually an x86_64, but could be anything, really (f.e. building directly
# on a Raspberry Pi implies that it's the host)
KDIR ?= /lib/modules/$(shell uname -r)/build
endif
#---
# Compiler
CC := $(CROSS_COMPILE)gcc
#CC := clang
STRIP := ${CROSS_COMPILE}strip
PWD := $(shell pwd)
obj-m += ${FNAME_C}.o
#--- Debug or production mode?
# Set the MYDEBUG variable accordingly to y/n resp. We keep it off (n) by default.
# (Actually, debug info is always going to be generated when you build the
# module on a debug kernel, where CONFIG_DEBUG_INFO is defined, making this
# setting of the ccflags-y (or the older EXTRA_CFLAGS) variable mostly redundant
# (besides the still useful -DDEBUG).
# This simply helps us influence the build on a production kernel, forcing
# generation of debug symbols, if so required. Also, realize that the DEBUG
# macro is turned on by many CONFIG_*DEBUG* options; hence, we use a different
# macro var name, MYDEBUG).
MYDEBUG := n
DBG_STRIP := y
ifeq (${MYDEBUG}, y)
# https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags
# EXTRA_CFLAGS deprecated; use ccflags-y
ccflags-y += -DDEBUG -g -ggdb -gdwarf-4 -Wall -fno-omit-frame-pointer -fvar-tracking-assignments
DBG_STRIP := n
else
ccflags-y += -UDEBUG
endif
# We always keep the dynamic debug facility enabled; this allows us to turn
# dynamically turn on/off debug printk's later... To disable it simply comment
# out the following line
ccflags-y += -DDYNAMIC_DEBUG_MODULE
KMODDIR ?= /lib/modules/$(shell uname -r)
# Gain access to kernel configs
include $(KDIR)/.config
# Strip the module? Note:
# a) Only strip debug symbols else it won't load correctly
# b) WARNING! Don't strip modules when using CONFIG_MODULE_SIG* crytographic security
ifdef CONFIG_MODULE_SIG
DBG_STRIP := n
endif
ifdef CONFIG_MODULE_SIG_ALL
DBG_STRIP := n
endif
ifdef CONFIG_MODULE_SIG_FORCE
DBG_STRIP := n
endif
all:
@echo
@echo '--- Building : KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} ccflags-y="${ccflags-y}" MYDEBUG=${MYDEBUG} DBG_STRIP=${DBG_STRIP} ---'
@${CC} --version|head -n1
@echo
make -C $(KDIR) M=$(PWD) modules
if [ "${DBG_STRIP}" = "y" ]; then \
${STRIP} --strip-debug ${FNAME_C}.ko ; \
fi
install:
@echo
@echo "--- installing ---"
@echo " [First, invoking the 'make' ]"
make
@echo
@echo " [Now for the 'sudo make install' ]"
sudo make -C $(KDIR) M=$(PWD) modules_install
sudo depmod
@echo " [If !debug and !(module signing), stripping debug info from ${KMODDIR}/extra/${FNAME_C}.ko]"
if [ "${DBG_STRIP}" = "y" ]; then \
sudo ${STRIP} --strip-debug ${KMODDIR}/extra/${FNAME_C}.ko ; \
fi
nsdeps:
@echo "--- nsdeps (namespace dependencies resolution; for possibly importing ns's) ---"
make -C $(KDIR) M=$(PWD) nsdeps
clean:
@echo
@echo "--- cleaning ---"
@echo
make -C $(KDIR) M=$(PWD) clean
# from 'indent'; comment out if you want the backup kept
rm -f *~
# Any usermode programs to build? Insert the build target(s) below
#--------------- More (useful) targets! -------------------------------
INDENT := indent
# code-style : "wrapper" target over the following kernel code style targets
code-style:
make indent
make checkpatch
# indent- "beautifies" C code - to conform to the the Linux kernel
# coding style guidelines.
# Note! original source file(s) is overwritten, so we back it up.
indent:
ifeq (,$(shell which indent))
$(error ERROR: install indent first)
endif
@echo
@echo "--- applying kernel code style indentation with indent ---"
@echo
mkdir bkp 2> /dev/null; cp -f *.[chsS] bkp/
${INDENT} -linux --line-length95 *.[chsS]
# add source files as required
# Detailed check on the source code styling / etc
checkpatch:
make clean
@echo
@echo "--- kernel code style check with checkpatch.pl ---"
@echo
$(KDIR)/scripts/checkpatch.pl --no-tree -f --max-line-length=95 *.[ch]
# add source files as required
#--- Static Analysis
# sa : "wrapper" target over the following kernel static analyzer targets
sa:
make sa_sparse
make sa_gcc
make sa_flawfinder
make sa_cppcheck
# static analysis with sparse
sa_sparse:
ifeq (,$(shell which sparse))
$(error ERROR: install sparse first)
endif
make clean
@echo
@echo "--- static analysis with sparse ---"
@echo
# If you feel it's too much, use C=1 instead
# NOTE: deliberately IGNORING warnings from kernel headers!
make -Wsparse-all C=2 CHECK="/usr/bin/sparse --os=linux --arch=$(ARCH)" -C $(KDIR) M=$(PWD) modules 2>&1 |egrep -v "^\./include/.*\.h|^\./arch/.*\.h"
# static analysis with gcc
sa_gcc:
make clean
@echo
@echo "--- static analysis with gcc ---"
@echo
make W=1 -C $(KDIR) M=$(PWD) modules
# static analysis with flawfinder
sa_flawfinder:
ifeq (,$(shell which flawfinder))
$(error ERROR: install flawfinder first)
endif
make clean
@echo
@echo "--- static analysis with flawfinder ---"
@echo
flawfinder *.[ch]
# static analysis with cppcheck
sa_cppcheck:
ifeq (,$(shell which cppcheck))
$(error ERROR: install cppcheck first)
endif
make clean
@echo
@echo "--- static analysis with cppcheck ---"
@echo
cppcheck -v --force --enable=all -i .tmp_versions/ -i *.mod.c -i bkp/ --suppress=missingIncludeSystem .
# Packaging: just generates a tar.xz of the source as of now
tarxz-pkg:
rm -f ../${FNAME_C}.tar.xz 2>/dev/null
make clean
@echo
@echo "--- packaging ---"
@echo
tar caf ../${FNAME_C}.tar.xz *
ls -l ../${FNAME_C}.tar.xz
@echo '=== package created: ../$(FNAME_C).tar.xz ==='
@echo ' TIP: When extracting, to extract into a directory with the same name as the tar file, do this:'
@echo ' tar -xvf ${FNAME_C}.tar.xz --one-top-level'
help:
@echo '=== Makefile Help : additional targets available ==='
@echo
@echo 'TIP: Type make <tab><tab> to show all valid targets'
@echo 'FYI: KDIR=${KDIR} ARCH=${ARCH} CROSS_COMPILE=${CROSS_COMPILE} ccflags-y="${ccflags-y}" MYDEBUG=${MYDEBUG} DBG_STRIP=${DBG_STRIP}'
@echo
@echo '--- 'usual' kernel LKM targets ---'
@echo 'typing "make" or "all" target : builds the kernel module object (the .ko)'
@echo 'install : installs the kernel module(s) to INSTALL_MOD_PATH (default here: /lib/modules/$(shell uname -r)/).'
@echo ' : Takes care of performing debug-only symbols stripping iff MYDEBUG=n and not using module signature'
@echo 'nsdeps : namespace dependencies resolution; for possibly importing namespaces'
@echo 'clean : cleanup - remove all kernel objects, temp files/dirs, etc'
@echo
@echo '--- kernel code style targets ---'
@echo 'code-style : "wrapper" target over the following kernel code style targets'
@echo ' indent : run the $(INDENT) utility on source file(s) to indent them as per the kernel code style'
@echo ' checkpatch : run the kernel code style checker tool on source file(s)'
@echo
@echo '--- kernel static analyzer targets ---'
@echo 'sa : "wrapper" target over the following kernel static analyzer targets'
@echo ' sa_sparse : run the static analysis sparse tool on the source file(s)'
@echo ' sa_gcc : run gcc with option -W1 ("Generally useful warnings") on the source file(s)'
@echo ' sa_flawfinder : run the static analysis flawfinder tool on the source file(s)'
@echo ' sa_cppcheck : run the static analysis cppcheck tool on the source file(s)'
@echo 'TIP: use Coccinelle as well: https://www.kernel.org/doc/html/v6.1/dev-tools/coccinelle.html'
@echo
@echo '--- kernel dynamic analysis targets ---'
@echo 'da_kasan : DUMMY target: this is to remind you to run your code with the dynamic analysis KASAN tool enabled; requires configuring the kernel with CONFIG_KASAN On, rebuild and boot it'
@echo 'da_lockdep : DUMMY target: this is to remind you to run your code with the dynamic analysis LOCKDEP tool (for deep locking issues analysis) enabled; requires configuring the kernel with CONFIG_PROVE_LOCKING On, rebuild and boot it'
@echo 'TIP: Best to build a debug kernel with several kernel debug config options turned On, boot via it and run all your test cases'
@echo
@echo '--- misc targets ---'
@echo 'tarxz-pkg : tar and compress the LKM source files as a tar.xz into the dir above; allows one to transfer and build the module on another system'
@echo ' TIP: When extracting, to extract into a directory with the same name as the tar file, do this:'
@echo ' tar -xvf ${FNAME_C}.tar.xz --one-top-level'
@echo 'help : this help target'

120
ch13/3_lockfree/thrdshowall_rcu/thrd_showall_rcu.c Normal file
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/*
* ch13/3_lockfree/thrdshowall_rcu/thrd_showall_rcu.c
***************************************************************
* This program is part of the source code released for the book
* "Linux Kernel Programming" 2E
* (c) Author: Kaiwan N Billimoria
* Publisher: Packt
* GitHub repository:
* https://github.com/PacktPublishing/Linux-Kernel-Programming_2E
*
* From: Ch 13 : Kernel Synchronization, Part 2
****************************************************************
* Brief Description:
* This kernel module is based upon our earlier kernel module here:
* ch13/4_lockdep/fixed_thrdshow_eg/
* We had "fixed it" by using the task_{un}lock() pair of APIs to provide
* synchronization. However, this wasn't an ideal solution as it introduced
* the possibility of a race, plus, the task_{un}lock() routines employ a
* spinlock that’s effective for only some of the task structure members.
*
* So, here, we do a proper fix by employing lockfree RCU! It's as-is very
* efficient for read-mostly situations, which this certainly qualifies as.
* Moreover, here, as we don’t ever modify any task structure's content,
* we even eliminate the need for write protection via a spinlock.
*
* For details, please refer the book, Ch 13.
*/
#define pr_fmt(fmt) "%s:%s(): " fmt, KBUILD_MODNAME, __func__
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h> /* current() */
#include <linux/version.h>
#if LINUX_VERSION_CODE > KERNEL_VERSION(4, 10, 0)
#include <linux/sched/signal.h>
#endif
MODULE_AUTHOR("Kaiwan N Billimoria");
MODULE_DESCRIPTION("LKP 2E book: ch13/3_lockfree/thrdshowall_rcu/:"
" Proper fix to the earlier buggy demos to display all threads by iterating over the task list, using RCU");
MODULE_LICENSE("Dual MIT/GPL");
MODULE_VERSION("0.2");
static int showthrds_buggy(void)
{
struct task_struct *g, *t; /* 'g' : process ptr; 't': thread ptr */
int nr_thrds = 1, total = 0;
#define BUFMAX 256
#define TMPMAX 128
char buf[BUFMAX], tmp[TMPMAX], tasknm[TASK_COMM_LEN];
const char hdr[] =
"--------------------------------------------------------------------------------\n"
" TGID PID current stack-start Thread Name MT? # thrds\n"
"--------------------------------------------------------------------------------\n";
pr_info("%s", hdr);
rcu_read_lock(); /* This triggers off an RCU read-side critical section; ensure
* you are non-blocking within it!
*/
do_each_thread(g, t) { /* 'g' : process ptr; 't': thread ptr */
get_task_struct(t); /* take a reference to the task struct */
snprintf(buf, BUFMAX-1, "%6d %6d ", g->tgid, t->pid);
/* task_struct addr and kernel-mode stack addr */
snprintf(tmp, TMPMAX-1, " 0x%px", t);
strncat(buf, tmp, TMPMAX);
snprintf(tmp, TMPMAX-1, " 0x%px", t->stack);
strncat(buf, tmp, TMPMAX);
if (!g->mm) // kernel thread
snprintf(tmp, sizeof(tasknm)+3, " [%16s]", tasknm);
else
snprintf(tmp, sizeof(tasknm)+3, " %16s ", tasknm);
strncat(buf, tmp, TMPMAX);
/* Is this the "main" thread of a multithreaded process?
* We check by seeing if (a) it's a userspace thread,
* (b) it's TGID == it's PID, and (c), there are >1 threads in
* the process.
* If so, display the number of threads in the overall process
* to the right..
*/
nr_thrds = get_nr_threads(g);
if (g->mm && (g->tgid == t->pid) && (nr_thrds > 1)) {
snprintf(tmp, TMPMAX-1, " %3d", nr_thrds);
strncat(buf, tmp, TMPMAX);
}
snprintf(tmp, 2, "\n");
strncat(buf, tmp, 2);
pr_info("%s", buf);
total++;
memset(buf, 0, sizeof(buf));
memset(tmp, 0, sizeof(tmp));
put_task_struct(t); /* release reference to the task struct */
} while_each_thread(g, t);
rcu_read_unlock();
return total;
}
static int __init thrd_showall_buggy_init(void)
{
int total;
pr_info("inserted\n");
total = showthrds_buggy();
pr_info("total # of threads on the system: %d\n", total);
return 0; /* success */
}
static void __exit thrd_showall_buggy_exit(void)
{
pr_info("removed\n");
}
module_init(thrd_showall_buggy_init);
module_exit(thrd_showall_buggy_exit);

99
ch13/3_lockfree/thrdshowall_rcu/using_rcu.patch Normal file
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@@ -0,0 +1,99 @@
--- ../../4_lockdep/fixed_thrdshow_eg/thrd_showall_fixed.c 2023-11-20 10:07:37.541117473 +0530
+++ thrd_showall_rcu.c 2023-11-20 10:08:18.791021075 +0530
@@ -1,5 +1,5 @@
/*
- * ch13/3_lockdep/buggy_thrdshow_eg/thrd_showall_buggy.c
+ * ch13/3_lockfree/thrdshowall_rcu/thrd_showall_rcu.c
***************************************************************
* This program is part of the source code released for the book
* "Linux Kernel Programming" 2E
@@ -11,15 +11,17 @@
* From: Ch 13 : Kernel Synchronization, Part 2
****************************************************************
* Brief Description:
- * This kernel module is based upon our earlier kernel module from Ch 6:
- * ch6/foreach/thrd_showall/thrd_showall.c.
- * Earlier (in the buggy version), we refactored it to use the
- * get_task_comm() routine to retrieve the name of the thread, it's buggy!
- * The bug turns out to be a recursive locking issue, *detected by lockdep*.
+ * This kernel module is based upon our earlier kernel module here:
+ * ch13/4_lockdep/fixed_thrdshow_eg/
+ * We had "fixed it" by using the task_{un}lock() pair of APIs to provide
+ * synchronization. However, this wasn't an ideal solution as it introduced
+ * the possibility of a race, plus, the task_{un}lock() routines employ a
+ * spinlock that’s effective for only some of the task structure members.
*
- * So now let's fix it.
- * Here, we fix the deadlock by first unlocking the relevant lock (struct
- * task_struct alloc_lock), then calling get_task_comm() and then locking it.
+ * So, here, we do a proper fix by employing lockfree RCU! It's as-is very
+ * efficient for read-mostly situations, which this certainly qualifies as.
+ * Moreover, here, as we don’t ever modify any task structure's content,
+ * we even eliminate the need for write protection via a spinlock.
*
* For details, please refer the book, Ch 13.
*/
@@ -34,8 +36,8 @@
#endif
MODULE_AUTHOR("Kaiwan N Billimoria");
-MODULE_DESCRIPTION("LKP 2E book: ch13/4_lockdep/fixed_thrdshow_eg/:"
-" FIX to the earlier buggy demo to display all threads by iterating over the task list");
+MODULE_DESCRIPTION("LKP 2E book: ch13/3_lockfree/thrdshowall_rcu/:"
+" Proper fix to the earlier buggy demos to display all threads by iterating over the task list, using RCU");
MODULE_LICENSE("Dual MIT/GPL");
MODULE_VERSION("0.2");
@@ -52,9 +54,12 @@
"--------------------------------------------------------------------------------\n";
pr_info("%s", hdr);
+
+ rcu_read_lock(); /* This triggers off an RCU read-side critical section; ensure
+ * you are non-blocking within it!
+ */
do_each_thread(g, t) { /* 'g' : process ptr; 't': thread ptr */
get_task_struct(t); /* take a reference to the task struct */
- task_lock(t); /*** task lock taken here! ***/
snprintf(buf, BUFMAX-1, "%6d %6d ", g->tgid, t->pid);
/* task_struct addr and kernel-mode stack addr */
@@ -63,17 +68,6 @@
snprintf(tmp, TMPMAX-1, " 0x%px", t->stack);
strncat(buf, tmp, TMPMAX);
- /* In the 'buggy' ver of this code, LOCKDEP did catch a deadlock here !!
- * (at the point that get_task_comm() was invoked).
- * The reason's clear: get_task_comm() attempts to take the very same lock
- * that we just took above via task_lock(t); !! This is obvious self-deadlock...
- * So, we fix it here by first unlocking it, calling get_task_comm(), and
- * then re-locking it.
- */
- task_unlock(t);
- get_task_comm(tasknm, t);
- task_lock(t);
-
if (!g->mm) // kernel thread
snprintf(tmp, sizeof(tasknm)+3, " [%16s]", tasknm);
else
@@ -100,9 +94,9 @@
total++;
memset(buf, 0, sizeof(buf));
memset(tmp, 0, sizeof(tmp));
- task_unlock(t);
put_task_struct(t); /* release reference to the task struct */
} while_each_thread(g, t);
+ rcu_read_unlock();
return total;
}
@@ -113,8 +107,7 @@
pr_info("inserted\n");
total = showthrds_buggy();
- pr_info("total # of threads on the system: %d\n",
- total);
+ pr_info("total # of threads on the system: %d\n", total);
return 0; /* success */
}