[Bug 204426] Processes terminating cannot access memory

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Mon Feb 29 15:14:48 UTC 2016


--- Comment #56 from Konstantin Belousov <kib at FreeBSD.org> ---
(In reply to Robert Blayzor from comment #55)
The uprintf_signal data was useful, thanks.

It is quite clean that the issue occured in the child after the
multithreaded fork.  An evidence is in the 'CN' flags (copy on write
and need copy) for all map entries of the process, except the stack.
The number of stacks mapped also suggests that the parent only had one
thread executing during the fork.  This is confirmed also by the
backtrace from the core, but for different reasons I trust the core

The fault occured on the stack access, as indicated by the fault
address.  What is very interesting is the error code 7, which is
hardware data indicating that this was user-mode write to the page
mapped read-only.  Which is again consistent with the state after

What I do not understand is why page fault handler did not performed
COW and changed the page permission to writeable, which it should, due
to rw permission on the map entry.

Could you, please, apply the attached debugging patch on top of the
used source and provide me the same data as now, i.e. procstat -v code
and kernel messages from the patch and uprintf_signal.

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