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Like other csets, init_css_set's dfl_cgrp is initialized when the cset gets linked. init_css_set gets linked in cgroup_init(). This has been fine till now but the recently added basic CPU usage accounting may end up accessing dfl_cgrp of init before cgroup_init() leading to the following oops. SELinux: Initializing. BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0 IP: account_system_index_time+0x60/0x90 PGD 0 P4D 0 Oops: 0000 [#1] SMP Modules linked in: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc2-00003-g041cd64 #10 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS +1.9.3-20161025_171302-gandalf 04/01/2014 task: ffffffff81e10480 task.stack: ffffffff81e00000 RIP: 0010:account_system_index_time+0x60/0x90 RSP: 0000:ffff880011e03cb8 EFLAGS: 00010002 RAX: ffffffff81ef8800 RBX: ffffffff81e10480 RCX: 0000000000000003 RDX: 0000000000000000 RSI: 00000000000f4240 RDI: 0000000000000000 RBP: ffff880011e03cc0 R08: 0000000000010000 R09: 0000000000000000 R10: 0000000000000020 R11: 0000003b9aca0000 R12: 000000000001c100 R13: 0000000000000000 R14: ffffffff81e10480 R15: ffffffff81e03cd8 FS: 0000000000000000(0000) GS:ffff880011e00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000000b0 CR3: 0000000001e09000 CR4: 00000000000006b0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <IRQ> account_system_time+0x45/0x60 account_process_tick+0x5a/0x140 update_process_times+0x22/0x60 tick_periodic+0x2b/0x90 tick_handle_periodic+0x25/0x70 timer_interrupt+0x15/0x20 __handle_irq_event_percpu+0x7e/0x1b0 handle_irq_event_percpu+0x23/0x60 handle_irq_event+0x42/0x70 handle_level_irq+0x83/0x100 handle_irq+0x6f/0x110 do_IRQ+0x46/0xd0 common_interrupt+0x9d/0x9d Fix it by statically initializing init_css_set.dfl_cgrp so that init's default cgroup is accessible from the get-go. Fixes: 041cd640b2f3 ("cgroup: Implement cgroup2 basic CPU usage accounting") Reported-by: “kbuild-all@01.org” <kbuild-all@01.org> Signed-off-by: Tejun Heo <tj@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.