Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Hi Philippe, >> >> Jan Kiszka wrote: >> >>> Just ran into this with CONFIG_IPIPE_DEBUG_CONTEXT (maybe due to some >>> bug of my own): >> >> Here is some code to trigger the issue reliably: >> >> #include <sys/mman.h> >> #include <native/task.h> >> >> void task_fnct(void *arg) >> { >> rt_task_delete(NULL); >> } >> >> main() >> { >> RT_TASK task; >> mlockall(MCL_CURRENT|MCL_FUTURE); >> rt_task_spawn(&task, "task", 0, 10, 0, task_fnct, NULL); >> } >> >> >> >>> [ 102.616000] I-pipe: Detected illicit call from domain 'Xenomai' >>> [ 102.616000] into a service reserved for domain 'Linux' and below. >>> [ 102.616000] c741bdc8 00000000 00000000 c8860ef8 c741bdec c0105683 >>> c032c200 c13fe22c >>> [ 102.616000] c0361f00 c741be08 c01519ed c032f5b8 c032c742 c03380b3 >>> c8885100 c78beac0 >>> [ 102.616000] c741be14 c0142ce9 c7a80b30 c741be3c c884d075 c885f150 >>> c8860ef8 c741be3c >>> [ 102.616000] Call Trace: >>> [ 102.616000] [<c0104d9f>] show_trace_log_lvl+0x1f/0x40 >>> [ 102.616000] [<c0104e71>] show_stack_log_lvl+0xb1/0xe0 >>> [ 102.616000] [<c0105683>] show_stack+0x33/0x40 >>> [ 102.616000] [<c01519ed>] ipipe_check_context+0xad/0xc0 >>> [ 102.616000] [<c0142ce9>] module_put+0x19/0x90 >>> [ 102.616000] [<c884d075>] xnshadow_unmap+0xb5/0x130 [xeno_nucleus] >>> [ 102.616000] [<c8871dc5>] __shadow_delete_hook+0x25/0x30 [xeno_native] >>> [ 102.616000] [<c8842f78>] xnpod_schedule+0xb58/0x12f0 [xeno_nucleus] >>> [ 102.616000] [<c8844bfb>] xnpod_delete_thread+0x2cb/0x3d0 [xeno_nucleus] >>> [ 102.616000] [<c886f5bd>] rt_task_delete+0x20d/0x220 [xeno_native] >>> >>> I would dare to say that module_put in xnshadow_unmap is not well placed >>> as it can wakeup a Linux process. The module ref-counter maintenance >>> needs some postponing, I guess. >> >> Attached is a patch proposal. It solves the issue by postponing the >> module_put via a new schedule_linux_call. Note that this approach issues >> LO_WAKEUP_REQ where the old test (p->state != TASK_RUNNING) would not >> have done so. I don't see negative side effects yet, and I'm furthermore >> not sure of the old code was handling SMP scenarios safely (What if the >> thread to be unmapped was running on different CPU than xnshadow_unmap? >> How to ensure test-atomicity then?). > > This one counts as mine! I am Ok with the fix, but IMHO, the > "if(p->state != TASK_RUNNING)" probably has a reason, so I would leave > it in the new implementation. >
But then I need some official declaration, that this test cannot race with whatever in case the target task runs on another CPU. I tried to direct my brain along this twisted path, but stopped before it started hurting too much (others would call it laziness). :) Jan
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