Messages in this thread | | | Date | Wed, 23 Apr 2014 10:26:00 +0900 | From | Masami Hiramatsu <> | Subject | Re: ftrace/kprobes: Warning when insmod two modules |
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(2014/04/22 17:35), Takao Indoh wrote: >>> >> But the text is already RO, so it causes panic. We need to call notifier >>> >> before setting it RO. Or should we unset RO temporarily in >>> >> ftrace_process_locs()? >> > >> > Perhaps, IMHO, ftrace needs to change the module RW in ftrace_init_module and >> > makes it RO after modifying the module text. > Hmm..., I think the same problem occurs if we set module RW in > ftrace_init_module(). > > <insmod module B> > init_module > load_module > complete_formation > set_section_ro_nx -------------------------------------- (1) > set_section_ro_nx -------------------------------------- (2) > blocking_notifier_call_chain > ftrace_module_notify_enter > ftrace_init_module --------------------------------- (3) > ftrace_process_locs > mutex_lock(&ftrace_lock) ------------------------ (4) > ftrace_update_code > __ftrace_replace_code > ftrace_make_nop > ftrace_modify_code_direct > do_ftrace_mod_code > probe_kernel_write -------------------- (5) > > > The text of module B is set to RO at (1) and (2) by Rusty's patch. And > even if we change it to RW at (3), it set to RO again by another module > while module B is waiting at (4). > > So, we need to set module to RW somewhere after get ftrace_lock, maybe > in ftrace_update_code()?
Agreed. That should be done in a protected (critical) region, and the region must be protected by correct lock. It seems that the ftrace_lock is not a correct one.
Thank you,
-- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com
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