Gilles Chanteperdrix wrote: > Philippe Gerum wrote: > > On Mon, 2007-02-12 at 00:07 +0100, Gilles Chanteperdrix wrote: > > > Philippe Gerum wrote: > > > > On Sun, 2007-02-11 at 23:13 +0100, Jan Kiszka wrote: > > > > > Hi, > > > > > > > > > > while testing 2.6.20 with RTnet, I got this kernel BUG during the > slave > > > > > startup procedure: > > > > > > > > > > <4>[ 137.799234] TDMA: calibrated master-to-slave packet delay: 34 > us (min/max: 33/38 us) > > > > > <4>[ 142.291455] BUG: at kernel/fork.c:993 copy_process() > > > > > <4>[ 142.291585] [<c0103a8f>] show_trace_log_lvl+0x1f/0x40 > > > > > <4>[ 142.291767] [<c0104237>] show_trace+0x17/0x20 > > > > > <4>[ 142.291896] [<c010432b>] dump_stack+0x1b/0x20 > > > > > <4>[ 142.292026] [<c0111e94>] copy_process+0x914/0x13d0 > > > > > <4>[ 142.292190] [<c0112b80>] do_fork+0x70/0x1b0 > > > > > <4>[ 142.292323] [<c0101078>] sys_clone+0x38/0x40 > > > > > <4>[ 142.292620] [<c010320f>] syscall_call+0x7/0xb > > > > > <4>[ 142.292747] ======================= > > > > > <3>[ 142.292860] BUG: sleeping function called from invalid > context at mm/slab.c:3034 > > > > > <4>[ 142.293052] in_atomic():0, irqs_disabled():1 > > > > ^^^^ > > > > > > > > Typical of something going wrong in entry.S. > > > > > > You mean, interrupts are not really disabled when forking ? :-) > > > > > > > Eh, mmmh, no. Hopefully. > > > > > So, I am afraid the new fpu_counter optimization is buggy: if a task > > > forks with fpu_counter greater than 5 and is preempted right after > > > prepare_to_copy in dup_task_struct, when the system switches back to > > > this task, the task FPU context will be restored and TS_USEDFPU set in > > > the task flags, thereby voiding the effect of prepare_to_copy. > > > > > > > You mean that the parent FPU context would leak into the child's one? > > Yes, something like that. The result is random segfaults, I do not > remember exactly why. > > > Well, maybe the LKML people would like to know about this. As a > > sidenote, I don't see anything bad with your latest counter-measure > > disabling this optimization in Xenomai's context switch code, even in > > the bugous case above. Right? > > Right, if there are random segfaults, they will not be xenomai's fault. >
I'm currently sorting the symptoms again, or better I'm looking where they went to. 2.6.20 just decided to work normally again, 2.6.19 needs a re-check. It appears now that the tracer played an important role, but I'm not 100% sure yet. I'll keep you posted. Jan
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