From: mscfd <mscfd@gmx.net>
To: fortran@gcc.gnu.org
Subject:
Date: Wed, 10 Mar 2021 18:34:32 +0000 (UTC) [thread overview]
Message-ID: <856aeaf7-defa-4797-a0e2-d4d5e07f5cc6@gmx.net> (raw)
> which version of gfortran, and which operating system?
I have seen this on two different Linux distros on x86 with a recently compiled version, but also some time ago with an older gfortran 10 version.
Using helgrind on a simple omp do loop with write to a character variable, I get some possible data races in Libgfortran/io/unit.c. There a newunits array is allocated and possibly reallocated in "newunit_alloc". According to the lock outputs from helgrind I see that this routine is called even if output into character variable is done. Now "newunit_alloc" uses a lock to avoid having several thread all over the place. But newunit_free also writes to newunits array. And this routine does not obtain a lock itself (see comment in unit.c) So in theory it can happen that newunit_alloc reallocated newunits, and newunit_free writes to it just at this time. As I also use 18 threads the initial size of 16 does not suffice and reallocation does probably indeed happen.
Also acces to newunit_lwi is not protected as well (and complained about by helgrind).
Could it be that the corresponding write routine in transfer.c which calls newunit_free does not obtain the necessary lock. I cannot find it (which does not count much).
Any thoughts?
Martin
next reply other threads:[~2021-03-10 18:35 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 18:34 mscfd [this message]
2021-03-11 7:48 ` Richard Biener
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