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Two small updates to ptrace_stop():

Browse source 
- Add a comment to explain that the preempt_disable() before unlocking
     tasklist lock is not a correctness problem and just avoids the tracer
     to preempt the tracee before the tracee schedules out.
 
   - Make that preempt_disable() conditional on PREEMPT_RT=n.
 
     RT enabled kernels cannot disable preemption at this point because
     cgroup_enter_frozen() and sched_submit_work() acquire spinlocks or
     rwlocks which are substituted by sleeping locks on RT. Acquiring a
     sleeping lock in a preemption disable region is obviously not possible.
 
     This obviously brings back the potential slowdown of ptrace() for RT
     enabled kernels, but that's a price to be payed for latency guarantees.
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Merge tag 'core-core-2023-10-29-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull core updates from Thomas Gleixner:
 "Two small updates to ptrace_stop():

   - Add a comment to explain that the preempt_disable() before
     unlocking tasklist lock is not a correctness problem and just
     avoids the tracer to preempt the tracee before the tracee schedules
     out.

   - Make that preempt_disable() conditional on PREEMPT_RT=n.

     RT enabled kernels cannot disable preemption at this point because
     cgroup_enter_frozen() and sched_submit_work() acquire spinlocks or
     rwlocks which are substituted by sleeping locks on RT. Acquiring a
     sleeping lock in a preemption disable region is obviously not
     possible.

     This obviously brings back the potential slowdown of ptrace() for
     RT enabled kernels, but that's a price to be paid for latency
     guarantees"

* tag 'core-core-2023-10-29-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  signal: Don't disable preemption in ptrace_stop() on PREEMPT_RT
  signal: Add a proper comment about preempt_disable() in ptrace_stop()
This commit is contained in:
Linus Torvalds 2023-10-30 17:03:32 -10:00
commit 9cc6fea175
1 changed files with 28 additions and 5 deletions
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