Messages in this thread Patch in this message |  | | | From | Sripathi Kodi <> | | Subject | [PREEMPT_RT] [PATCH] scheduling with irqs disabled: strace/0x00000000/2011 | | Date | Fri, 20 Apr 2007 11:45:07 +0530 |
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Hi,
While running strace on some testcase running on -rt kernel (2.6.20-rt8 and 2.6.21-rc6-rt0), I have seen the following BUG:
BUG: scheduling with irqs disabled: strace/0x00000000/2011 caller is rt_spin_lock_slowlock+0x102/0x1af Call Trace: [<ffffffff8026d828>] dump_trace+0xbd/0x3d8 [<ffffffff8026db87>] show_trace+0x44/0x6d [<ffffffff8026ddc8>] dump_stack+0x13/0x15 [<ffffffff80264dc6>] schedule+0x87/0x10b [<ffffffff80265b06>] rt_spin_lock_slowlock+0x102/0x1af [<ffffffff802661af>] rt_spin_lock+0x1f/0x21 [<ffffffff8029af0c>] force_sig_info+0x26/0xb5 [<ffffffff8029b018>] force_sig_specific+0x11/0x13 [<ffffffff80298659>] ptrace_attach+0xdf/0x10b [<ffffffff802986d7>] sys_ptrace+0x52/0xb8 [<ffffffff8025f42c>] tracesys+0x151/0x1be [<00000034ecec71c9>] --------------------------- | preempt count: 00000000 ] | 0-level deep critical section nesting: ---------------------------------------- In ptrace_attach, this is what happens:
task_lock local_irq_disable write_lock(tasklist_lock) Using trylocks. Some work __ptrace_link Send SIGSTOP to target thread write_unlock_irq(tasklist_lock) task_unlock
On -rt, write_unlock_irq doesn't do local_irq_enable. Even if it did, we are calling it after sending SIGSTOP to target thread. To fix the problem, I think we should call write_unlock(tasklist_lock) and local_irq_enable() instead of write_unlock_irq. Also, we should call them before calling force_sig_specific(). I think there is no need to hold the tasklist lock while calling force_sig_specific(). Is my understanding correct? Alternatively, can we remove the call to local_irq_disable() in -rt kernel?
For the non-rt kernel too, I think we should do write_unlock_irq(tasklist_lock) before sending SIGSTOP.
The following patch solves the problem for me.
Thanks and regards, Sripathi.
Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>
--- linux-2.6.21-rc6-rt0-org/kernel/ptrace.c 2007-04-06 08:06:56.000000000 +0530 +++ linux-2.6.21-rc6-rt0/kernel/ptrace.c 2007-04-19 18:18:40.000000000 +0530 @@ -205,10 +205,16 @@ repeat: __ptrace_link(task, current); + write_unlock(&tasklist_lock); + local_irq_enable(); + force_sig_specific(SIGSTOP, task); + goto out2; bad: - write_unlock_irq(&tasklist_lock); + write_unlock(&tasklist_lock); + local_irq_enable(); +out2: task_unlock(task); out: return retval; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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