On Oct 28 16:22, David McFarland wrote: > For a long time I've been struggling with intermittent deadlocks and > segfaults in emacs, seemingly related to invoking child processes. I > recently found a reliable way to reproduce one such deadlock: > > - install clean cygwin with: emacs-w32, clang > - install flycheck from elpa > - grab some non trivial C header e.g.: > $ cp /usr/include/stdio.h test.h > - $ emacs -q test.h > - start flycheck: > (progn (package-initialize) > (require 'flycheck) > (flycheck-mode)) > - add a character to the start of the first line > - wait for flygheck to complete > - repeat the last two steps until a deadlock occurs > > Breaking in gdb showed the main thread in `cygheap_protect.acquire ()`, > from either _cfree or _cmalloc. The thread holding the mutex was always > "flasio", and it would either be continually segfaulting or looping in > _cfree. > > I added some debug prints to cygheap and determined that it flasio was > double-freeing an atomic_write_buf. I added some more prints and found > that it was two different fhandler objects freeing the same buffer. > > I then found that `fhandler_base_overlapped::copyto` would clear the > buffer pointer after the copy, but none of the derived classes (pipe, > fifo) did. > > Attached is a patch which clears the buffer pointers when copying pipes > and fifos. > > It would probably be safer to move the buffer clear to a `operator=`, > but I wanted to keep the patch as simple as possible and avoid > refactoring.
Excellent detective work, thanks for the patch! Pushed. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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