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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, bp@alien8.de, corbet@lwn.net,
	gregkh@linuxfoundation.org, jeyu@kernel.org, linux-mm@kvack.org,
	linux@rasmusvillemoes.dk, mcgrof@kernel.org,
	mm-commits@vger.kernel.org, ndesaulniers@google.com,
	tiwai@suse.de, torvalds@linux-foundation.org
Subject: [patch 70/91] init/initramfs.c: do unpacking asynchronously
Date: Thu, 06 May 2021 18:05:42 -0700	[thread overview]
Message-ID: <20210507010542.Wg91mG_Wr%akpm@linux-foundation.org> (raw)
In-Reply-To: <20210506180126.03e1baee7ca52bedb6cc6003@linux-foundation.org>

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: init/initramfs.c: do unpacking asynchronously

Patch series "background initramfs unpacking, and CONFIG_MODPROBE_PATH", v3.

These two patches are independent, but better-together.

The second is a rather trivial patch that simply allows the developer to
change "/sbin/modprobe" to something else - e.g.  the empty string, so
that all request_module() during early boot return -ENOENT early, without
even spawning a usermode helper, needlessly synchronizing with the
initramfs unpacking.

The first patch delegates decompressing the initramfs to a worker thread,
allowing do_initcalls() in main.c to proceed to the device_ and late_
initcalls without waiting for that decompression (and populating of
rootfs) to finish.  Obviously, some of those later calls may rely on the
initramfs being available, so I've added synchronization points in the
firmware loader and usermodehelper paths - there might be other places
that would need this, but so far no one has been able to think of any
places I have missed.

There's not much to win if most of the functionality needed during boot is
only available as modules.  But systems with a custom-made .config and
initramfs can boot faster, partly due to utilizing more than one cpu
earlier, partly by avoiding known-futile modprobe calls (which would still
trigger synchronization with the initramfs unpacking, thus eliminating
most of the first benefit).


This patch (of 2):

Most of the boot process doesn't actually need anything from the
initramfs, until of course PID1 is to be executed.  So instead of doing
the decompressing and populating of the initramfs synchronously in
populate_rootfs() itself, push that off to a worker thread.

This is primarily motivated by an embedded ppc target, where unpacking
even the rather modest sized initramfs takes 0.6 seconds, which is long
enough that the external watchdog becomes unhappy that it doesn't get
attention soon enough.  By doing the initramfs decompression in a worker
thread, we get to do the device_initcalls and hence start petting the
watchdog much sooner.

Normal desktops might benefit as well.  On my mostly stock Ubuntu kernel,
my initramfs is a 26M xz-compressed blob, decompressing to around 126M. 
That takes almost two seconds:

[    0.201454] Trying to unpack rootfs image as initramfs...
[    1.976633] Freeing initrd memory: 29416K

Before this patch, these lines occur consecutively in dmesg.  With this
patch, the timestamps on these two lines is roughly the same as above, but
with 172 lines inbetween - so more than one cpu has been kept busy doing
work that would otherwise only happen after the populate_rootfs()
finished.

Should one of the initcalls done after rootfs_initcall time (i.e., device_
and late_ initcalls) need something from the initramfs (say, a kernel
module or a firmware blob), it will simply wait for the initramfs
unpacking to be done before proceeding, which should in theory make this
completely safe.

But if some driver pokes around in the filesystem directly and not via one
of the official kernel interfaces (i.e.  request_firmware*(),
call_usermodehelper*) that theory may not hold - also, I certainly might
have missed a spot when sprinkling wait_for_initramfs().  So there is an
escape hatch in the form of an initramfs_async= command line parameter.

Link: https://lkml.kernel.org/r/20210313212528.2956377-1-linux@rasmusvillemoes.dk
Link: https://lkml.kernel.org/r/20210313212528.2956377-2-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/admin-guide/kernel-parameters.txt |   12 ++++
 drivers/base/firmware_loader/main.c             |    2 
 include/linux/initrd.h                          |    2 
 init/initramfs.c                                |   38 +++++++++++++-
 init/main.c                                     |    1 
 kernel/umh.c                                    |    2 
 6 files changed, 56 insertions(+), 1 deletion(-)

--- a/Documentation/admin-guide/kernel-parameters.txt~init-initramfsc-do-unpacking-asynchronously
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -1839,6 +1839,18 @@
 			initcall functions.  Useful for debugging built-in
 			modules and initcalls.
 
+	initramfs_async= [KNL]
+			Format: <bool>
+			Default: 1
+			This parameter controls whether the initramfs
+			image is unpacked asynchronously, concurrently
+			with devices being probed and
+			initialized. This should normally just work,
+			but as a debugging aid, one can get the
+			historical behaviour of the initramfs
+			unpacking being completed before device_ and
+			late_ initcalls.
+
 	initrd=		[BOOT] Specify the location of the initial ramdisk
 
 	initrdmem=	[KNL] Specify a physical address and size from which to
--- a/drivers/base/firmware_loader/main.c~init-initramfsc-do-unpacking-asynchronously
+++ a/drivers/base/firmware_loader/main.c
@@ -15,6 +15,7 @@
 #include <linux/kernel_read_file.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/initrd.h>
 #include <linux/timer.h>
 #include <linux/vmalloc.h>
 #include <linux/interrupt.h>
@@ -504,6 +505,7 @@ fw_get_filesystem_firmware(struct device
 	if (!path)
 		return -ENOMEM;
 
+	wait_for_initramfs();
 	for (i = 0; i < ARRAY_SIZE(fw_path); i++) {
 		size_t file_size = 0;
 		size_t *file_size_ptr = NULL;
--- a/include/linux/initrd.h~init-initramfsc-do-unpacking-asynchronously
+++ a/include/linux/initrd.h
@@ -20,8 +20,10 @@ extern void free_initrd_mem(unsigned lon
 
 #ifdef CONFIG_BLK_DEV_INITRD
 extern void __init reserve_initrd_mem(void);
+extern void wait_for_initramfs(void);
 #else
 static inline void __init reserve_initrd_mem(void) {}
+static inline void wait_for_initramfs(void) {}
 #endif
 
 extern phys_addr_t phys_initrd_start;
--- a/init/initramfs.c~init-initramfsc-do-unpacking-asynchronously
+++ a/init/initramfs.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/init.h>
+#include <linux/async.h>
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/types.h>
@@ -541,6 +542,14 @@ static int __init keepinitrd_setup(char
 __setup("keepinitrd", keepinitrd_setup);
 #endif
 
+static bool __initdata initramfs_async = true;
+static int __init initramfs_async_setup(char *str)
+{
+	strtobool(str, &initramfs_async);
+	return 1;
+}
+__setup("initramfs_async=", initramfs_async_setup);
+
 extern char __initramfs_start[];
 extern unsigned long __initramfs_size;
 #include <linux/initrd.h>
@@ -658,7 +667,7 @@ static void __init populate_initrd_image
 }
 #endif /* CONFIG_BLK_DEV_RAM */
 
-static int __init populate_rootfs(void)
+static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
 {
 	/* Load the built in initramfs */
 	char *err = unpack_to_rootfs(__initramfs_start, __initramfs_size);
@@ -693,6 +702,33 @@ done:
 	initrd_end = 0;
 
 	flush_delayed_fput();
+}
+
+static ASYNC_DOMAIN_EXCLUSIVE(initramfs_domain);
+static async_cookie_t initramfs_cookie;
+
+void wait_for_initramfs(void)
+{
+	if (!initramfs_cookie) {
+		/*
+		 * Something before rootfs_initcall wants to access
+		 * the filesystem/initramfs. Probably a bug. Make a
+		 * note, avoid deadlocking the machine, and let the
+		 * caller's access fail as it used to.
+		 */
+		pr_warn_once("wait_for_initramfs() called before rootfs_initcalls\n");
+		return;
+	}
+	async_synchronize_cookie_domain(initramfs_cookie + 1, &initramfs_domain);
+}
+EXPORT_SYMBOL_GPL(wait_for_initramfs);
+
+static int __init populate_rootfs(void)
+{
+	initramfs_cookie = async_schedule_domain(do_populate_rootfs, NULL,
+						 &initramfs_domain);
+	if (!initramfs_async)
+		wait_for_initramfs();
 	return 0;
 }
 rootfs_initcall(populate_rootfs);
--- a/init/main.c~init-initramfsc-do-unpacking-asynchronously
+++ a/init/main.c
@@ -1561,6 +1561,7 @@ static noinline void __init kernel_init_
 
 	kunit_run_all_tests();
 
+	wait_for_initramfs();
 	console_on_rootfs();
 
 	/*
--- a/kernel/umh.c~init-initramfsc-do-unpacking-asynchronously
+++ a/kernel/umh.c
@@ -27,6 +27,7 @@
 #include <linux/ptrace.h>
 #include <linux/async.h>
 #include <linux/uaccess.h>
+#include <linux/initrd.h>
 
 #include <trace/events/module.h>
 
@@ -107,6 +108,7 @@ static int call_usermodehelper_exec_asyn
 
 	commit_creds(new);
 
+	wait_for_initramfs();
 	retval = kernel_execve(sub_info->path,
 			       (const char *const *)sub_info->argv,
 			       (const char *const *)sub_info->envp);
_

  parent reply	other threads:[~2021-05-07  1:05 UTC|newest]

Thread overview: 119+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07  1:01 incoming Andrew Morton
2021-05-07  1:02 ` [patch 01/91] alpha: eliminate old-style function definitions Andrew Morton
2021-05-07  1:02 ` [patch 02/91] alpha: csum_partial_copy.c: add function prototypes from <net/checksum.h> Andrew Morton
2021-05-07  1:02 ` [patch 03/91] fs/proc/generic.c: fix incorrect pde_is_permanent check Andrew Morton
2021-05-07  1:02 ` [patch 04/91] proc: save LOC in __xlate_proc_name() Andrew Morton
2021-05-07  2:24   ` Linus Torvalds
2021-05-07  1:02 ` [patch 05/91] proc: mandate ->proc_lseek in "struct proc_ops" Andrew Morton
2021-05-07  1:02 ` [patch 06/91] proc: delete redundant subset=pid check Andrew Morton
2021-05-07  1:02 ` [patch 07/91] selftests: proc: test subset=pid Andrew Morton
2021-05-07  1:02 ` [patch 08/91] proc/sysctl: fix function name error in comments Andrew Morton
2021-05-07  1:02 ` [patch 09/91] include: remove pagemap.h from blkdev.h Andrew Morton
2021-05-07  1:02 ` [patch 10/91] kernel.h: drop inclusion in bitmap.h Andrew Morton
2021-05-07  1:02 ` [patch 11/91] linux/profile.h: remove unnecessary declaration Andrew Morton
2021-05-07  1:02 ` [patch 12/91] kernel/async.c: fix pr_debug statement Andrew Morton
2021-05-07  1:02 ` [patch 13/91] kernel/cred.c: make init_groups static Andrew Morton
2021-05-07  1:02 ` [patch 14/91] tools: disable -Wno-type-limits Andrew Morton
2021-05-07  1:02 ` [patch 15/91] tools: bitmap: sync function declarations with the kernel Andrew Morton
2021-05-07  1:02 ` [patch 16/91] tools: sync BITMAP_LAST_WORD_MASK() macro " Andrew Morton
2021-05-07  1:02 ` [patch 17/91] arch: rearrange headers inclusion order in asm/bitops for m68k, sh and h8300 Andrew Morton
2021-05-07  1:02 ` [patch 18/91] lib: extend the scope of small_const_nbits() macro Andrew Morton
2021-05-07  1:03 ` [patch 19/91] tools: sync small_const_nbits() macro with the kernel Andrew Morton
2021-05-07  1:03 ` [patch 20/91] lib: inline _find_next_bit() wrappers Andrew Morton
2021-05-07  1:03 ` [patch 21/91] tools: sync find_next_bit implementation Andrew Morton
2021-05-07  1:03 ` [patch 22/91] lib: add fast path for find_next_*_bit() Andrew Morton
2021-05-07  1:03 ` [patch 23/91] lib: add fast path for find_first_*_bit() and find_last_bit() Andrew Morton
2021-05-07  1:03 ` [patch 24/91] tools: sync lib/find_bit implementation Andrew Morton
2021-05-07  1:03 ` [patch 25/91] MAINTAINERS: add entry for the bitmap API Andrew Morton
2021-05-07  1:03 ` [patch 26/91] lib/bch.c: fix a typo in the file bch.c Andrew Morton
2021-05-07  1:03 ` [patch 27/91] lib: fix inconsistent indenting in process_bit1() Andrew Morton
2021-05-07  1:03 ` [patch 28/91] lib/list_sort.c: fix typo in function description Andrew Morton
2021-05-07  1:03 ` [patch 29/91] lib/genalloc.c: fix a typo Andrew Morton
2021-05-07  1:03 ` [patch 30/91] lib: crc8: pointer to data block should be const Andrew Morton
2021-05-07  1:03 ` [patch 31/91] lib: stackdepot: turn depot_lock spinlock to raw_spinlock Andrew Morton
2021-05-07  1:03 ` [patch 32/91] lib/percpu_counter: tame kernel-doc compile warning Andrew Morton
2021-05-07  1:03 ` [patch 33/91] lib/genalloc: add parameter description to fix doc " Andrew Morton
2021-05-07  1:03 ` [patch 34/91] lib: parser: clean up kernel-doc Andrew Morton
2021-05-07  1:03 ` [patch 35/91] include/linux/compat.h: remove unneeded declaration from COMPAT_SYSCALL_DEFINEx() Andrew Morton
2021-05-07  1:03 ` [patch 36/91] checkpatch: warn when missing newline in return sysfs_emit() formats Andrew Morton
2021-05-07  1:03 ` [patch 37/91] checkpatch: exclude four preprocessor sub-expressions from MACRO_ARG_REUSE Andrew Morton
2021-05-07  1:04 ` [patch 38/91] checkpatch: improve ALLOC_ARRAY_ARGS test Andrew Morton
2021-05-07  1:04 ` [patch 39/91] kselftest: introduce new epoll test case Andrew Morton
2021-05-07  1:04 ` [patch 40/91] fs/epoll: restore waking from ep_done_scan() Andrew Morton
2021-05-07  1:04 ` [patch 41/91] isofs: fix fall-through warnings for Clang Andrew Morton
2021-05-07  1:04 ` [patch 42/91] fs/nilfs2: fix misspellings using codespell tool Andrew Morton
2021-05-07  1:04 ` [patch 43/91] nilfs2: fix typos in comments Andrew Morton
2021-05-07  1:04 ` [patch 44/91] hpfs: replace one-element array with flexible-array member Andrew Morton
2021-05-07  1:04 ` [patch 45/91] do_wait: make PIDTYPE_PID case O(1) instead of O(n) Andrew Morton
2021-05-07  1:04 ` [patch 46/91] kernel/fork.c: simplify copy_mm() Andrew Morton
2021-05-07  1:04 ` [patch 47/91] kernel/fork.c: fix typos Andrew Morton
2021-05-07  1:04 ` [patch 48/91] kernel/crash_core: add crashkernel=auto for vmcore creation Andrew Morton
2021-05-07  7:25   ` Linus Torvalds
2021-05-08  3:13     ` Baoquan He
2021-05-08  3:29       ` Baoquan He
2021-05-07  8:16   ` David Hildenbrand
2021-05-08  8:51     ` Baoquan He
2021-05-08  9:22       ` David Hildenbrand
2021-05-10  4:53         ` Baoquan He
2021-05-10  8:32           ` David Hildenbrand
2021-05-10 10:43             ` Baoquan He
2021-05-10 11:01               ` David Hildenbrand
2021-05-10 11:44                 ` Dave Young
2021-05-10 11:56                   ` David Hildenbrand
2021-05-11 13:36                     ` Baoquan He
2021-05-11 16:31                       ` Mike Rapoport
2021-05-11 17:07                         ` David Hildenbrand
2021-05-12 14:51                           ` Baoquan He
2021-05-12 15:07                             ` David Hildenbrand
2021-05-13  5:04                               ` Baoquan He
2021-05-12 19:03                             ` Kairui Song
2021-05-17  8:22                             ` David Hildenbrand
2021-05-18  8:49                               ` Baoquan He
2021-05-18  8:51                                 ` David Hildenbrand
2021-05-18  9:24                                   ` Dave Young
2021-05-12 14:13                         ` Baoquan He
2021-05-12  7:42                     ` Dave Young
2021-05-07  1:04 ` [patch 49/91] kexec: add kexec reboot string Andrew Morton
2021-05-07  1:04 ` [patch 50/91] kernel: kexec_file: fix error return code of kexec_calculate_store_digests() Andrew Morton
2021-05-07  1:04 ` [patch 51/91] kexec: dump kmessage before machine_kexec Andrew Morton
2021-05-07  1:04 ` [patch 52/91] gcov: combine common code Andrew Morton
2021-05-07  1:04 ` [patch 53/91] gcov: simplify buffer allocation Andrew Morton
2021-05-07  1:04 ` [patch 54/91] gcov: use kvmalloc() Andrew Morton
2021-05-07  1:04 ` [patch 55/91] gcov: clang: drop support for clang-10 and older Andrew Morton
2021-05-07  1:04 ` [patch 56/91] smp: kernel/panic.c - silence warnings Andrew Morton
2021-05-07  1:05 ` [patch 57/91] delayacct: clear right task's flag after blkio completes Andrew Morton
2021-05-07  1:05 ` [patch 58/91] gdb: lx-symbols: store the abspath() Andrew Morton
2021-05-07  1:05 ` [patch 59/91] scripts/gdb: document lx_current is only supported by x86 Andrew Morton
2021-05-07  1:05 ` [patch 60/91] scripts/gdb: add lx_current support for arm64 Andrew Morton
2021-05-07  1:05 ` [patch 61/91] kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources Andrew Morton
2021-05-07  1:05 ` [patch 62/91] kernel/resource: make walk_mem_res() find all busy IORESOURCE_MEM resources Andrew Morton
2021-05-07  1:05 ` [patch 63/91] kernel/resource: remove first_lvl / siblings_only logic Andrew Morton
2021-05-07  1:05 ` [patch 64/91] kernel/resource: allow region_intersects users to hold resource_lock Andrew Morton
2021-05-07  1:05 ` [patch 65/91] kernel/resource: refactor __request_region to allow external locking Andrew Morton
2021-05-07  1:05 ` [patch 66/91] kernel/resource: fix locking in request_free_mem_region Andrew Morton
2021-05-07  1:05 ` [patch 67/91] selftests: remove duplicate include Andrew Morton
2021-05-07  1:05 ` [patch 68/91] kernel/async.c: stop guarding pr_debug() statements Andrew Morton
2021-05-07  1:05 ` [patch 69/91] kernel/async.c: remove async_unregister_domain() Andrew Morton
2021-05-07  1:05 ` Andrew Morton [this message]
2021-05-07  1:05 ` [patch 71/91] modules: add CONFIG_MODPROBE_PATH Andrew Morton
2021-05-07  1:05 ` [patch 72/91] ipc/sem.c: mundane typo fixes Andrew Morton
2021-05-07  1:05 ` [patch 73/91] mm: fix some typos and code style problems Andrew Morton
2021-05-07  1:05 ` [patch 74/91] drivers/char: remove /dev/kmem for good Andrew Morton
2021-05-07  1:06 ` [patch 75/91] mm: remove xlate_dev_kmem_ptr() Andrew Morton
2021-05-07  1:06 ` [patch 76/91] mm/vmalloc: remove vwrite() Andrew Morton
2021-05-07  1:06 ` [patch 77/91] arm: print alloc free paths for address in registers Andrew Morton
2021-05-07  1:06 ` [patch 78/91] scripts/spelling.txt: add "overlfow" Andrew Morton
2021-05-07  1:06 ` [patch 79/91] scripts/spelling.txt: add "diabled" typo Andrew Morton
2021-05-07  1:06 ` [patch 80/91] scripts/spelling.txt: add "overflw" Andrew Morton
2021-05-07  1:06 ` [patch 81/91] mm/slab.c: fix spelling mistake "disired" -> "desired" Andrew Morton
2021-05-07  1:06 ` [patch 82/91] include/linux/pgtable.h: few spelling fixes Andrew Morton
2021-05-07  1:06 ` [patch 83/91] kernel/umh.c: fix some spelling mistakes Andrew Morton
2021-05-07  1:06 ` [patch 84/91] kernel/user_namespace.c: fix typos Andrew Morton
2021-05-07  1:06 ` [patch 85/91] kernel/up.c: fix typo Andrew Morton
2021-05-07  1:06 ` [patch 86/91] kernel/sys.c: " Andrew Morton
2021-05-07  1:06 ` [patch 87/91] fs: fat: fix spelling typo of values Andrew Morton
2021-05-07  1:06 ` [patch 88/91] ipc/sem.c: spelling fix Andrew Morton
2021-05-07  1:06 ` [patch 89/91] treewide: remove editor modelines and cruft Andrew Morton
2021-05-07  1:06 ` [patch 90/91] mm: fix typos in comments Andrew Morton
2021-05-07  1:06 ` [patch 91/91] " Andrew Morton
2021-05-07  7:12 ` incoming Linus Torvalds

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