Messages in this thread | | | Date | Thu, 16 May 2013 15:59:38 +0200 | From | Alexander Holler <> | Subject | Re: BUG: tty: memory corruption through tty_release/tty_ldisc_release |
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Am 16.05.2013 15:47, schrieb Peter Hurley: > On 05/16/2013 02:45 AM, Alexander Holler wrote: >> Hello, >> >> after some pain because the "big step" (ecbbfd4) happened while the >> support for my AMD CPU was broken and thus git bisect hit a series of >> kernels which didn't boot, I've finally found the cause for a memory >> corruption: tty_ldisc_release(). >> >> What happens is the following: >> >> tty_port is self-destructing, that means it destroys itself in >> tty_port.c:tty_port_destructor() when the last reference is gone. E.g. >> in case of rfcomm this happens with the call to tty->ops->close() in >> tty_io.c:tty_release(). >> >> The problem here is that tty_io.c:tty_release() calls >> tty_ldisc.c:tty_ldisc_release() which uses the tty_port to flush the >> ldisc work queues. >> >> In the best case this hits a BUG() in cancel_work_sync() but often it >> just causes a memory corruption without a BUG() got hit before. > > Hi Alexander, > > Actually, the problem is that tty->ops->close() shouldn't be > the last kref on the port. > > It doesn't look to me like device removal is being handled > properly. >
Maybe, but if so, that should be documented (and ideally prevented). Especially since it seemed to have been worked before tty_ports got introduced.
But I can't add much more to this discussion, as I'm rather a novice in regard to the tty subsystem. I even don't know much about the task sharing between tty, tty_port and tty_ldisc, except the stuff I found out because I got hit by that bug and therefor have read some of the sources.
Regards,
Alexander Holler
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