Revised version – the previous had a lock inversion, which could lead to
a deadlock, found by -fsanitize=thread. See transfer.c for the changes.
OK?
Tobias
On 11.03.21 10:42, Tobias Burnus wrote:
Hi all,
as found by Martin (thanks!) there is a race for newunit_free.
While that call is within the unitlock for the calls in io/unit.c,
the call in transfer.c did not use locks.
Additionally,
unit = get_gfc_unit (dtp->common.unit, do_create);
set_internal_unit (dtp, unit, kind);
gets first the unit (with proper locking when using the unit number
dtp->common.unit) but then in set_internal_unit it re-sets the
unit number to the same number without locking. That causes
race warnings and if the assignment is not atomic it is a true race.
OK for mainline? What about GCC 10?
As Martin notes in the email thread and in the PR there are more
race warnings (and likely true race issues).
Tobias
Fortran: Fix libgfortran I/O race with newunit_free [PR99529]
libgfortran/ChangeLog:
* io/transfer.c (st_read_done_worker, st_write_done_worker):
Call unlock_unit here, add unit_lock lock around newunit_free call.
(st_read_done, st_write_done): Only call unlock_unit when not
calling the worker function.
* io/unit.c (set_internal_unit): Don't reset the unit_number
to the same number as this cause race warnings.
diff --git a/libgfortran/io/transfer.c b/libgfortran/io/transfer.c
index 27bee9d4e01..71a935652e3 100644
--- a/libgfortran/io/transfer.c
+++ b/libgfortran/io/transfer.c
@@ -4339,6 +4339,7 @@ export_proto(st_read_done);
void
st_read_done_worker (st_parameter_dt *dtp)
{
+ bool free_newunit = false;
finalize_transfer (dtp);
free_ionml (dtp);
@@ -4358,7 +4359,7 @@ st_read_done_worker (st_parameter_dt *dtp)
free (dtp->u.p.current_unit->ls);
dtp->u.p.current_unit->ls = NULL;
}
- newunit_free (dtp->common.unit);
+ free_newunit = true;
}
if (dtp->u.p.unit_is_internal || dtp->u.p.format_not_saved)
{
@@ -4366,6 +4367,14 @@ st_read_done_worker (st_parameter_dt *dtp)
free_format (dtp);
}
}
+ unlock_unit (dtp->u.p.current_unit);
+ if (free_newunit)
+ {
+ /* Avoid inverse lock issues by placing after unlock_unit. */
+ LOCK (_lock);
+ newunit_free (dtp->common.unit);
+ UNLOCK (_lock);
+ }
}
void
@@ -4382,11 +4391,10 @@ st_read_done (st_parameter_dt *dtp)
if (dtp->u.p.async)
enqueue_done (dtp->u.p.current_unit->au, AIO_READ_DONE);
}
+ unlock_unit (dtp->u.p.current_unit);
}
else
- st_read_done_worker (dtp);
-
- unlock_unit (dtp->u.p.current_unit);
+ st_read_done_worker (dtp); /* Calls unlock_unit. */
}
library_end ();
@@ -4406,6 +4414,7 @@ st_write (st_parameter_dt *dtp)
void
st_write_done_worker (st_parameter_dt *dtp)
{
+ bool free_newunit = false;
finalize_transfer (dtp);
if (dtp->u.p.current_unit != NULL
@@ -4446,7 +4455,7 @@ st_write_done_worker (st_parameter_dt *dtp)
free (dtp->u.p.current_unit->ls);
dtp->u.p.current_unit->ls = NULL;
}
- newunit_free (dtp->common.unit);
+ free_newunit = true;
}
if (dtp->u.p.unit_is_internal || dtp->u.p.format_not_saved)
{
@@ -4454,6 +4463,14 @@ st_write_done_worker (st_parameter_dt *dtp)
free_format (dtp);
}
}
+ unlock_unit (dtp->u.p.current_unit);
+ if (free_newunit)
+ {
+ /* Avoid inverse lock issues by placing after unlock_unit. */
+ LOCK (_lock);
+ newunit_free (dtp->common.unit);
+ UNLOCK (_lock);
+ }
}
extern void st_write_done (st_parameter_dt *);
@@ -4476,11 +4493,10 @@ st_write_done (st_parameter_dt *dtp)
if (dtp->u.p.async)
enqueue_done (dtp->u.p.current_unit->au, AIO_WRITE_DONE);
}
+ unlock_unit (dtp->u.p.current_unit);
}
else
- st_write_done_worker (dtp);
-
- unlock_unit (dtp->u.p.current_unit);
+ st_write_done_worker (dtp); /* Calls unlock_unit. */
}
library_end ();
diff --git a/libgfortran/io/unit.c b/libgfortran/io/unit.c
index 2ea664331bc..b0cc6ab2301 100644
--- a/libgfortran/io/unit.c
+++ b/libgfortran/io/unit.c
@@ -456,7 +456,6 @@ set_internal_unit (st_parameter_dt *dtp, gfc_unit *iunit, int kind)
{
gfc_offset start_record = 0;
- iunit->unit_number = dtp->common.unit;
iunit->recl = dtp->internal_unit_len;
iunit->internal_unit = dtp->internal_unit;
iunit->internal_unit_len = dtp->internal_unit_len;
