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[v2,0/5] ptrace-vs-PREEMPT_RT and freezer rewrite

Message ID 20220421150248.667412396@infradead.org (mailing list archive)
Headers show
Series ptrace-vs-PREEMPT_RT and freezer rewrite | expand

Message

Peter Zijlstra April 21, 2022, 3:02 p.m. UTC 
Find here a new posting of the ptrace and freezer patches :-)

The majority of the changes are in patch 2, which with much feedback from Oleg
and Eric has changed lots.

I'm hoping we're converging on something agreeable.

---
 drivers/acpi/x86/s2idle.c         |  12 +-
 drivers/android/binder.c          |   4 +-
 drivers/media/pci/pt3/pt3.c       |   4 +-
 drivers/scsi/scsi_transport_spi.c |   7 +-
 fs/cifs/inode.c                   |   4 +-
 fs/cifs/transport.c               |   5 +-
 fs/coredump.c                     |   5 +-
 fs/nfs/file.c                     |   3 +-
 fs/nfs/inode.c                    |  12 +-
 fs/nfs/nfs3proc.c                 |   3 +-
 fs/nfs/nfs4proc.c                 |  14 +--
 fs/nfs/nfs4state.c                |   3 +-
 fs/nfs/pnfs.c                     |   4 +-
 fs/xfs/xfs_trans_ail.c            |   8 +-
 include/linux/completion.h        |   1 +
 include/linux/freezer.h           | 244 ++------------------------------------
 include/linux/sched.h             |  49 ++++----
 include/linux/sched/jobctl.h      |  10 ++
 include/linux/sched/signal.h      |   5 +-
 include/linux/sunrpc/sched.h      |   7 +-
 include/linux/suspend.h           |   8 +-
 include/linux/umh.h               |   9 +-
 include/linux/wait.h              |  40 ++++++-
 init/do_mounts_initrd.c           |  10 +-
 kernel/cgroup/legacy_freezer.c    |  23 ++--
 kernel/exit.c                     |   4 +-
 kernel/fork.c                     |   5 +-
 kernel/freezer.c                  | 137 +++++++++++++++------
 kernel/futex/waitwake.c           |   8 +-
 kernel/hung_task.c                |   4 +-
 kernel/power/hibernate.c          |  35 ++++--
 kernel/power/main.c               |  18 +--
 kernel/power/process.c            |  10 +-
 kernel/power/suspend.c            |  12 +-
 kernel/power/user.c               |  24 ++--
 kernel/ptrace.c                   | 114 ++++++++++--------
 kernel/sched/completion.c         |   9 ++
 kernel/sched/core.c               |  24 ++--
 kernel/signal.c                   |  62 +++++++---
 kernel/time/hrtimer.c             |   4 +-
 kernel/umh.c                      |  18 ++-
 mm/khugepaged.c                   |   4 +-
 net/sunrpc/sched.c                |  12 +-
 net/unix/af_unix.c                |   8 +-
 44 files changed, 478 insertions(+), 528 deletions(-)

Comments

Sebastian Andrzej Siewior April 22, 2022, 5:43 p.m. UTC | #1 
On 2022-04-21 17:02:48 [+0200], Peter Zijlstra wrote:
> Find here a new posting of the ptrace and freezer patches :-)
> 
> The majority of the changes are in patch 2, which with much feedback from Oleg
> and Eric has changed lots.
> 
> I'm hoping we're converging on something agreeable.

I tested this under RT (had to remove the preempt-disable section in
ptrace_stop()) with ssdd [0]. It forks a few tasks and then
PTRACE_SINGLESTEPs them for a few iterations.

The following failures were reported by that tool:
| forktest#27/3790: EXITING, ERROR: wait on PTRACE_ATTACH saw a SIGCHLD count of 0, should be 1
| forktest#225/40029: EXITING, ERROR: wait on PTRACE_SINGLESTEP #22241: no SIGCHLD seen (signal count == 0), signo 5

very rarely. Then I managed to figure out that the latter error triggers
if I compile something large with a RT priority. Sadly it also happens
with my old ptrace hack (but I just noticed it). It didn't happen with
without RT (just the 5 patches applied).

I also managed to trigger this backtrace with RT:
|WARNING: CPU: 1 PID: 3748 at kernel/signal.c:2237 ptrace_stop+0x356/0x370
|Modules linked in:
|CPU: 1 PID: 3748 Comm: ssdd Not tainted 5.18.0-rc3-rt1+ #1
|Hardware name: Intel Corporation S2600CP/S2600CP, BIOS SE5C600.86B.02.03.0003.041920141333 04/19/2014
|RIP: 0010:ptrace_stop+0x356/0x370
|RSP: 0000:ffffc9000d277d98 EFLAGS: 00010246
|RAX: ffff888116d1e100 RBX: ffff888116d1e100 RCX: 0000000000000001
|RDX: 0000000000000001 RSI: 000000000000002e RDI: ffffffff822bdcc3
|RBP: ffff888116d1e100 R08: ffff88811ca99870 R09: 0000000000000001
|R10: ffff88811ca99910 R11: ffff88852ade2680 R12: ffffc9000d277e90
|R13: 0000000000000004 R14: ffff888116d1ed48 R15: 0000000000000000
|FS:  00007f0afdad4580(0000) GS:ffff88852aa40000(0000) knlGS:0000000000000000
|CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
|CR2: 00007f0afdad4508 CR3: 0000000558198006 CR4: 00000000000606e0
|Call Trace:
| <TASK>
| get_signal+0x553/0x870
| arch_do_signal_or_restart+0x31/0x7b0
| exit_to_user_mode_prepare+0xe4/0x110
| irqentry_exit_to_user_mode+0x5/0x20
| noist_exc_debug+0xe0/0x120
| asm_exc_debug+0x2b/0x30
|RSP: 002b:00007fffae964b70 EFLAGS: 00000346
|RAX: 0000000000000000 RBX: 00000000000000fc RCX: 00007f0afd9c0d35
|RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
|RBP: 00007fffae964e38 R08: 0000000000000000 R09: 00007fffae962a82
|R10: 00007f0afdad4850 R11: 0000000000000246 R12: 0000000000000000
|R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
| </TASK>

which is the WARN_ON_ONCE() in clear_traced_quiesce().

[0] https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git/tree/src/ssdd/ssdd.c

Sebastian
Eric W. Biederman April 22, 2022, 7:15 p.m. UTC | #2 
Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> On 2022-04-21 17:02:48 [+0200], Peter Zijlstra wrote:
>> Find here a new posting of the ptrace and freezer patches :-)
>> 
>> The majority of the changes are in patch 2, which with much feedback from Oleg
>> and Eric has changed lots.
>> 
>> I'm hoping we're converging on something agreeable.
>
> I tested this under RT (had to remove the preempt-disable section in
> ptrace_stop()) with ssdd [0]. It forks a few tasks and then
> PTRACE_SINGLESTEPs them for a few iterations.

Out of curiosity why did you need to remove the preempt_disable section
on PREEMPT_RT?  It should have lasted for just a moment until schedule
was called.

Eric
Sebastian Andrzej Siewior April 22, 2022, 9:13 p.m. UTC | #3 
On 2022-04-22 14:15:35 [-0500], Eric W. Biederman wrote:
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> 
> > On 2022-04-21 17:02:48 [+0200], Peter Zijlstra wrote:
> >> Find here a new posting of the ptrace and freezer patches :-)
> >> 
> >> The majority of the changes are in patch 2, which with much feedback from Oleg
> >> and Eric has changed lots.
> >> 
> >> I'm hoping we're converging on something agreeable.
> >
> > I tested this under RT (had to remove the preempt-disable section in
> > ptrace_stop()) with ssdd [0]. It forks a few tasks and then
> > PTRACE_SINGLESTEPs them for a few iterations.
> 
> Out of curiosity why did you need to remove the preempt_disable section
> on PREEMPT_RT?  It should have lasted for just a moment until schedule
> was called.

within that section spinlock_t locks are acquired. These locks are
sleeping locks on PREEMPT_RT and must not be acquired within a
preempt-disable section. (A spinlock_t lock does not disable preemption
on PREEMPT_RT.)

> Eric

Sebastian