Messages in this thread | | | Date | Mon, 13 Jun 2022 21:38:22 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: RFC: repeated insmod/rmmod and DEBUG_KOBJECT_RELEASE - do we care? |
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On Mon, Jun 13, 2022 at 07:02:39AM -0400, Paul Gortmaker wrote: > If a person has CONFIG_DEBUG_KOBJECT_RELEASE enabled, and runs a rather > questionable test suite doing a repeated modprobe followed by modprobe -r > it will eventually trigger a duplicate sysfs name warning: > > [ 1427.032646] kobject: 'usbserial_generic' (00000000c91a1c2c): kobject_release, parent 00000000890627c7 (delayed 4000) > [...] > [ 1430.110659] kobject: 'usbserial_generic' (00000000a633d9a5): kobject_add_internal: parent: 'drivers', set: 'drivers' > [ 1430.110667] sysfs: cannot create duplicate filename '/bus/usb/drivers/usbserial_generic' > [ 1430.110671] CPU: 2 PID: 1102 Comm: modprobe Not tainted 5.15.38 #7 > [ 1430.110678] Call Trace: > [ 1430.110685] dump_stack_lvl+0x33/0x42 > [ 1430.110693] sysfs_warn_dup+0x51/0x60 <---------- > [ 1430.110699] sysfs_create_dir_ns+0xb8/0xd0 > > For context to lkml readers, CONFIG_DEBUG_KOBJECT_RELEASE inserts a > random delay of between 2 and 5 seconds before freeing a kobject. > > In the above case, the free was delayed 4s by the DEBUG option, but we tried > to reconstruct the same sysfs entry in just 3s elapsed and hence it triggered > the namespace collision warning. > > I'm not convinced this warrants fixing, given the contrived nature of the > root only test, but I did at least want to get it on record, so maybe it > saves someone else some research time, given a similar report.
It's come up many many times in the past years, sorry you hit it again without realizing it.
> We could I guess, within the CONFIG_DEBUG_KOBJECT_RELEASE ifdef'd code use > kobject_rename() to add a "-zombie" suffix or something like that, but then > it might mask name space collisions people *do* want to see?
That wouldn't work as you would have rename collisions as well.
And that warning is just that, a warning that you did something foolish so the kernel is trying to say "don't do that". And doing a modprobe/rmmod constantly is a huge "don't do that" hint.
> As per above it was seen with usb-serial, but I suspect any driver with a > sysfs kobject could reproduce the issue. I also didn't reproduce on the > latest kernel but I can't imagine anything has changed in this area.
Yes, the module handling code has changed a bit, so it might have solved some of these things. But the root cause is still there, you are doing something odd/broken and the kernel warned you about it :)
thanks,
greg k-h
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