f2b31bb598
I've got two independent reports that cgroup_task_frozen() check in cgroup_exit() has been triggered by lkp libhugetlbfs-test and LTP ptrace01 tests. For example: [ 44.576072] WARNING: CPU: 1 PID: 3028 at kernel/cgroup/cgroup.c:5932 cgroup_exit+0x148/0x160 [ 44.577724] Modules linked in: crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel sr_mod cdrom bochs_drm sg ttm ata_generic pata_acpi ppdev drm_kms_helper snd_pcm syscopyarea aesni_intel snd_timer sysfillrect sysimgblt snd crypto_simd cryptd glue_helper soundcore fb_sys_fops joydev drm serio_raw pcspkr ata_piix libata i2c_piix4 floppy parport_pc parport ip_tables [ 44.583106] CPU: 1 PID: 3028 Comm: ptrace-write-hu Not tainted 5.1.0-rc3-00053-g9262503 #5 [ 44.584600] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [ 44.586116] RIP: 0010:cgroup_exit+0x148/0x160 [ 44.587135] Code: 0f 84 50 ff ff ff 48 8b 85 c8 0c 00 00 48 8b 78 70 e8 ec 2e 00 00 e9 3b ff ff ff f0 ff 43 60 0f 88 72 21 89 00 e9 48 ff ff ff <0f> 0b e9 1b ff ff ff e8 3c 73 f4 ff 66 90 66 2e 0f 1f 84 00 00 00 [ 44.590113] RSP: 0018:ffffb25702dcfd30 EFLAGS: 00010002 [ 44.591167] RAX: ffff96a7fee32410 RBX: ffff96a7ff1d6000 RCX: dead000000000200 [ 44.592446] RDX: ffff96a7ff1d6080 RSI: ffff96a7fec75290 RDI: ffff96a7fec75290 [ 44.593715] RBP: ffff96a7fec745c0 R08: ffff96a7fec74658 R09: 0000000000000000 [ 44.594985] R10: 0000000000000000 R11: 0000000000000001 R12: ffff96a7fec75101 [ 44.596266] R13: ffff96a7fec745c0 R14: ffff96a7ff3bde30 R15: ffff96a7fec75130 [ 44.597550] FS: 0000000000000000(0000) GS:ffff96a7dd700000(0000) knlGS:0000000000000000 [ 44.598950] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 [ 44.600098] CR2: 00000000f7a00000 CR3: 000000000d20e000 CR4: 00000000000406e0 [ 44.601417] Call Trace: [ 44.602777] do_exit+0x337/0xc40 [ 44.603677] do_group_exit+0x3a/0xa0 [ 44.604610] get_signal+0x12e/0x8d0 [ 44.605533] ? __switch_to_asm+0x40/0x70 [ 44.606503] do_signal+0x36/0x650 [ 44.607409] ? __switch_to_asm+0x40/0x70 [ 44.608383] ? __schedule+0x267/0x860 [ 44.609329] exit_to_usermode_loop+0x89/0xf0 [ 44.610349] do_fast_syscall_32+0x251/0x2e3 [ 44.611357] entry_SYSENTER_compat+0x7f/0x91 [ 44.612376] ---[ end trace e4ca5cfc4b7f7964 ]--- The problem is caused by the ptrace_signal() call in the for loop in get_signal(). There is a cgroup_enter_frozen() call inside ptrace_signal(), so after exit from ptrace_signal() the task->frozen bit might be set. In this case do_group_exit() can be called with the task->frozen bit set and trigger the warning. This is only place where we can leave the loop with the task->frozen bit set and without setting JOBCTL_TRAP_FREEZE and TIF_SIGPENDING. To resolve this problem, let's move cgroup_leave_frozen(true) call to just after the fatal label. If the task is going to die, the frozen bit must be cleared no matter how we get into this point. Reported-by: kernel test robot <rong.a.chen@intel.com> Reported-by: Qian Cai <cai@lca.pw> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Roman Gushchin <guro@fb.com> Signed-off-by: Tejun Heo <tj@kernel.org>
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 Restructured Text 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.