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David Vernet 0e7ffff1b8 scx: Fix raciness in scx_ops_bypass() scx_ops_bypass() can currently race on the ops enable / disable path as follows: 1. scx_ops_bypass(true) called on enable path, bypass depth is set to 1 2. An op on the init path exits, which schedules scx_ops_disable_workfn() 3. scx_ops_bypass(false) is called on the disable path, and bypass depth is decremented to 0 4. kthread is scheduled to execute scx_ops_disable_workfn() 5. scx_ops_bypass(true) called, bypass depth set to 1 6. scx_ops_bypass() races when iterating over CPUs While it's not safe to take any blocking locks on the bypass path, it is safe to take a raw spinlock which cannot be preempted. This patch therefore updates scx_ops_bypass() to use a raw spinlock to synchronize, and changes scx_ops_bypass_depth to be a regular int. Without this change, we observe the following warnings when running the 'exit' sched_ext selftest (sometimes requires a couple of runs): .[root@virtme-ng sched_ext]# ./runner -t exit ===== START ===== TEST: exit ... [ 14.935078] WARNING: CPU: 2 PID: 360 at kernel/sched/ext.c:4332 scx_ops_bypass+0x1ca/0x280 [ 14.935126] Modules linked in: [ 14.935150] CPU: 2 UID: 0 PID: 360 Comm: sched_ext_ops_h Not tainted 6.11.0-virtme #24 [ 14.935192] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 [ 14.935242] Sched_ext: exit (enabling+all) [ 14.935244] RIP: 0010:scx_ops_bypass+0x1ca/0x280 [ 14.935300] Code: ff ff ff e8 48 96 10 00 fb e9 08 ff ff ff c6 05 7b 34 e8 01 01 90 48 c7 c7 89 86 88 87 e8 be 1d f8 ff 90 0f 0b 90 90 eb 95 90 <0f> 0b 90 41 8b 84 24 24 0a 00 00 eb 97 90 0f 0b 90 41 8b 84 24 24 [ 14.935394] RSP: 0018:ffffb706c0957ce0 EFLAGS: 00010002 [ 14.935424] RAX: 0000000000000009 RBX: 0000000000000001 RCX: 00000000e3fb8b2a [ 14.935465] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff88a4c080 [ 14.935512] RBP: 0000000000009b56 R08: 0000000000000004 R09: 00000003f12e520a [ 14.935555] R10: ffffffff863a9795 R11: 0000000000000000 R12: ffff8fc5fec31300 [ 14.935598] R13: ffff8fc5fec31318 R14: 0000000000000286 R15: 0000000000000018 [ 14.935642] FS: 0000000000000000(0000) GS:ffff8fc5fe680000(0000) knlGS:0000000000000000 [ 14.935684] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 14.935721] CR2: 0000557d92890b88 CR3: 000000002464a000 CR4: 0000000000750ef0 [ 14.935765] PKRU: 55555554 [ 14.935782] Call Trace: [ 14.935802] <TASK> [ 14.935823] ? __warn+0xce/0x220 [ 14.935850] ? scx_ops_bypass+0x1ca/0x280 [ 14.935881] ? report_bug+0xc1/0x160 [ 14.935909] ? handle_bug+0x61/0x90 [ 14.935934] ? exc_invalid_op+0x1a/0x50 [ 14.935959] ? asm_exc_invalid_op+0x1a/0x20 [ 14.935984] ? raw_spin_rq_lock_nested+0x15/0x30 [ 14.936019] ? scx_ops_bypass+0x1ca/0x280 [ 14.936046] ? srso_alias_return_thunk+0x5/0xfbef5 [ 14.936081] ? __pfx_scx_ops_disable_workfn+0x10/0x10 [ 14.936111] scx_ops_disable_workfn+0x146/0xac0 [ 14.936142] ? finish_task_switch+0xa9/0x2c0 [ 14.936172] ? srso_alias_return_thunk+0x5/0xfbef5 [ 14.936211] ? __pfx_scx_ops_disable_workfn+0x10/0x10 [ 14.936244] kthread_worker_fn+0x101/0x2c0 [ 14.936268] ? __pfx_kthread_worker_fn+0x10/0x10 [ 14.936299] kthread+0xec/0x110 [ 14.936327] ? __pfx_kthread+0x10/0x10 [ 14.936351] ret_from_fork+0x37/0x50 [ 14.936374] ? __pfx_kthread+0x10/0x10 [ 14.936400] ret_from_fork_asm+0x1a/0x30 [ 14.936427] </TASK> [ 14.936443] irq event stamp: 21002 [ 14.936467] hardirqs last enabled at (21001): [<ffffffff863aa35f>] resched_cpu+0x9f/0xd0 [ 14.936521] hardirqs last disabled at (21002): [<ffffffff863dd0ba>] scx_ops_bypass+0x11a/0x280 [ 14.936571] softirqs last enabled at (20642): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0 [ 14.936622] softirqs last disabled at (20637): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0 [ 14.936672] ---[ end trace 0000000000000000 ]--- [ 14.953282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 14.953352] ------------[ cut here ]------------ [ 14.953383] WARNING: CPU: 2 PID: 360 at kernel/sched/ext.c:4335 scx_ops_bypass+0x1d8/0x280 [ 14.953428] Modules linked in: [ 14.953453] CPU: 2 UID: 0 PID: 360 Comm: sched_ext_ops_h Tainted: G W 6.11.0-virtme #24 [ 14.953505] Tainted: [W]=WARN [ 14.953527] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 [ 14.953574] RIP: 0010:scx_ops_bypass+0x1d8/0x280 [ 14.953603] Code: c6 05 7b 34 e8 01 01 90 48 c7 c7 89 86 88 87 e8 be 1d f8 ff 90 0f 0b 90 90 eb 95 90 0f 0b 90 41 8b 84 24 24 0a 00 00 eb 97 90 <0f> 0b 90 41 8b 84 24 24 0a 00 00 eb 92 f3 0f 1e fa 49 8d 84 24 f0 [ 14.953693] RSP: 0018:ffffb706c0957ce0 EFLAGS: 00010046 [ 14.953722] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000001 [ 14.953763] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8fc5fec31318 [ 14.953804] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 [ 14.953845] R10: ffffffff863a9795 R11: 0000000000000000 R12: ffff8fc5fec31300 [ 14.953888] R13: ffff8fc5fec31318 R14: 0000000000000286 R15: 0000000000000018 [ 14.953934] FS: 0000000000000000(0000) GS:ffff8fc5fe680000(0000) knlGS:0000000000000000 [ 14.953974] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 14.954009] CR2: 0000557d92890b88 CR3: 000000002464a000 CR4: 0000000000750ef0 [ 14.954052] PKRU: 55555554 [ 14.954068] Call Trace: [ 14.954085] <TASK> [ 14.954102] ? __warn+0xce/0x220 [ 14.954126] ? scx_ops_bypass+0x1d8/0x280 [ 14.954150] ? report_bug+0xc1/0x160 [ 14.954178] ? handle_bug+0x61/0x90 [ 14.954203] ? exc_invalid_op+0x1a/0x50 [ 14.954226] ? asm_exc_invalid_op+0x1a/0x20 [ 14.954250] ? raw_spin_rq_lock_nested+0x15/0x30 [ 14.954285] ? scx_ops_bypass+0x1d8/0x280 [ 14.954311] ? __mutex_unlock_slowpath+0x3a/0x260 [ 14.954343] scx_ops_disable_workfn+0xa3e/0xac0 [ 14.954381] ? __pfx_scx_ops_disable_workfn+0x10/0x10 [ 14.954413] kthread_worker_fn+0x101/0x2c0 [ 14.954442] ? __pfx_kthread_worker_fn+0x10/0x10 [ 14.954479] kthread+0xec/0x110 [ 14.954507] ? __pfx_kthread+0x10/0x10 [ 14.954530] ret_from_fork+0x37/0x50 [ 14.954553] ? __pfx_kthread+0x10/0x10 [ 14.954576] ret_from_fork_asm+0x1a/0x30 [ 14.954603] </TASK> [ 14.954621] irq event stamp: 21002 [ 14.954644] hardirqs last enabled at (21001): [<ffffffff863aa35f>] resched_cpu+0x9f/0xd0 [ 14.954686] hardirqs last disabled at (21002): [<ffffffff863dd0ba>] scx_ops_bypass+0x11a/0x280 [ 14.954735] softirqs last enabled at (20642): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0 [ 14.954782] softirqs last disabled at (20637): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0 [ 14.954829] ---[ end trace 0000000000000000 ]--- [ 15.022283] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 15.092282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 15.149282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) ok 1 exit # ===== END ===== And with it, the test passes without issue after 1000s of runs: .[root@virtme-ng sched_ext]# ./runner -t exit ===== START ===== TEST: exit DESCRIPTION: Verify we can cleanly exit a scheduler in multiple places OUTPUT: [ 7.412856] sched_ext: BPF scheduler "exit" enabled [ 7.427924] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 7.466677] sched_ext: BPF scheduler "exit" enabled [ 7.475923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 7.512803] sched_ext: BPF scheduler "exit" enabled [ 7.532924] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 7.586809] sched_ext: BPF scheduler "exit" enabled [ 7.595926] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 7.661923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) [ 7.723923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF) ok 1 exit # ===== END ===== ============================= RESULTS: PASSED: 1 SKIPPED: 0 FAILED: 0 Fixes: `f0e1a0643a` ("sched_ext: Implement BPF extensible scheduler class") Signed-off-by: David Vernet <void@manifault.com> Signed-off-by: Tejun Heo <tj@kernel.org>		2024-10-25 11:10:51 -10:00
arch	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
block	vfs-6.12.blocksize	2024-09-20 17:53:17 -07:00
certs	sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3	2024-09-20 19:52:48 +03:00
crypto	KEYS: prevent NULL pointer dereference in find_asymmetric_key()	2024-09-20 19:49:49 +03:00
Documentation	sched_ext: Documentation: Update instructions for running example schedulers	2024-10-08 08:49:18 -10:00
drivers	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
fs	Summary	2024-09-24 11:08:40 -07:00
include	I3C for 6.12	2024-09-24 12:53:54 -07:00
init	sched_ext: Initial pull request for v6.12	2024-09-21 09:44:57 -07:00
io_uring	for-6.12/io_uring-20240922	2024-09-24 11:11:38 -07:00
ipc	struct fd layout change (and conversion to accessor helpers)	2024-09-23 09:35:36 -07:00
kernel	scx: Fix raciness in scx_ops_bypass()	2024-10-25 11:10:51 -10:00
lib	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
LICENSES	LICENSES: add 0BSD license text	2024-09-01 20:43:24 -07:00
mm	lsm/stable-6.12 PR 20240923	2024-09-24 10:18:15 -07:00
net	NFSD 6.12 Release Notes	2024-09-23 12:01:45 -07:00
rust	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2024-09-05 20:37:20 -07:00
samples	Landlock updates for v6.12-rc1	2024-09-24 10:40:11 -07:00
scripts	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
security	Landlock updates for v6.12-rc1	2024-09-24 10:40:11 -07:00
sound	firewire updates for v6.12	2024-09-23 12:55:27 -07:00
tools	scx: Fix exit selftest to use custom DSQ	2024-10-25 07:03:36 -10:00
usr	initramfs: shorten cmd_initfs in usr/Makefile	2024-07-16 01:07:52 +09:00
virt	struct fd layout change (and conversion to accessor helpers)	2024-09-23 09:35:36 -07:00
.clang-format	Docs: Move clang-format from process/ to dev-tools/	2024-06-26 16:36:00 -06:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.editorconfig	.editorconfig: remove trim_trailing_whitespace option	2024-06-13 16:47:52 +02:00
.get_maintainer.ignore	Add Jeff Kirsher to .get_maintainer.ignore	2024-03-08 11:36:54 +00:00
.gitattributes	.gitattributes: set diff driver for Rust source code files	2023-05-31 17:48:25 +02:00
.gitignore	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
.mailmap	Summary	2024-09-24 11:08:40 -07:00
.rustfmt.toml	rust: add `.rustfmt.toml`	2022-09-28 09:02:20 +02:00
COPYING	COPYING: state that all contributions really are covered by this file	2020-02-10 13:32:20 -08:00
CREDITS	MAINTAINERS: Mark powerpc spufs as orphaned	2024-08-19 21:27:56 +10:00
Kbuild	Kbuild updates for v6.1	2022-10-10 12:00:45 -07:00
Kconfig	kbuild: ensure full rebuild when the compiler is updated	2020-05-12 13:28:33 +09:00
MAINTAINERS	Input updates for v6.12-rc0	2024-09-24 12:42:35 -07:00
Makefile	Kbuild updates for v6.12	2024-09-24 13:02:06 -07:00
README	README: Fix spelling	2024-03-18 03:36:32 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.