https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98046
Bug ID: 98046
Summary: lock in libpthread occurs with gcc-fortran and
atlas-lapack
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: anthony.debeus at gmail dot com
Target Milestone: ---
When running the following code under kernel 5.8.18-1-MANJARO (among others)
and gcc-fortran 10.2.0
PROGRAM bugs
USE badwrite
x=AC(0)
write(*,*) 'x: ',x ! this works
write (*,*) '0: ',AC(0) !this does not
STOP
END
MODULE badwrite
CONTAINS
function AC(m2) result(c)
INTEGER,INTENT(IN) :: m2
write(*,*) m2 !killer statement with lapack or blas linked ONLY with atlas
c = m2+3
end function AC
END MODULE badwrite
compiled with
gfortran -c -llapack badwrite.f90
gfortran -llapack badwrite.f90 bugs.f90
should result in
0
x: 3.0000000
0: 0
3.00000000
However with the -llapack library (or the blas library, and possibly other
external libraries)
the result is
0
x: 3.000000
(program hangs here)
Adding the -ggdb flag, running in gdb and interrupting with ^C results in
Starting program: /home/me/build/bugs.lib90/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
0
x: 3.00000000
^C
Program received signal SIGINT, Interrupt.
0x00007ffff6baddb0 in __lll_lock_wait () from /usr/lib/libpthread.so.0
The two writes are deadlocked.
Conditions:
(1) Only happens with an external library linked in, so
gfortran -c badwrite.f90
gfortran badwrite.f90 bugs.f90
runs normally without hanging
(2) Removing the write statement in the function AC also removes the hang.
(3) Separating the writes, as in the first statement with x=AC(0) then
write(*,*) x, removes the deadlock/hang
(4) When using the "regular" lapack and blas libraries, the problem does not
occur.
(5) The problem does not occur with pgfortran (aka nvfortran) 20.7-0 LLVM
(6) Changing kernels to 5.7 or 5.9 series on the same machine does not solve
the problem.
This problem was originally reported on
https://www.linuxquestions.org/questions/linux-general-1/lock-in-libpthread-occurs-only-on-one-arch-installation-only-with-gcc-fortran-4175685889/
before discovering that it was triggered by the combination of gcc+atlas
lapack. Because of condition (5) this is reported as a gcc-fortran bug.
