As this patch is rather obvious, I intent to commit it tomorrow
as obvious, unless there is an OK earlier or other comments :-)
(And backport to GCC 11 in a couple of days.)
Before PR100352 (r11-7647),
st_write_done did:
st_write_done_worker (dtd)
unlock_unit (dtp->u.p.current_unit);
but st_write_done_worker did:
LOCK (&unit_lock);
newunit_free (dtp->common.unit);
UNLOCK (&unit_lock);
And this locking could lead to a deadlock.
Hence, 'unlock_unit' has been moved to st_write_done_worker
before the LOCK (&unit_lock).
That solved the issue, but async I/O does not use this lock
but, in async.c's async_io():
LOCK (&au->lock);
st_write_done_worker (au->pdt);
UNLOCK (&au->io_lock);
Which worked before the previous patch fine, but now
there is a bogus unlock_unit() alias UNLOCK (&u->lock);
although the unit is not locked.
Solution: Guard the unlock_unit.
Tobias
PS: The thread sanitizer still complains about a potential
cross-thread deadlock, see new PR100371.
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Fortran: Async I/O - avoid unlocked unlocking [PR100352]
Follow up to PR100352, which moved unit unlocking to st_*_done_worker to
avoid lock order reversal; however, as async_io uses a different lock,
the (unlocked locked) unit lock shall not be unlocked there.
libgfortran/ChangeLog:
PR libgomp/100352
* io/transfer.c (st_read_done_worker, st_write_done_worker): Add new
arg whether to unlock unit.
(st_read_done, st_write_done): Call it with true.
* io/async.c (async_io): Call it with false.
* io/io.h (st_write_done_worker, st_read_done_worker): Update prototype.
libgfortran/io/async.c | 4 ++--
libgfortran/io/io.h | 4 ++--
libgfortran/io/transfer.c | 14 ++++++++------
3 files changed, 12 insertions(+), 10 deletions(-)
diff --git a/libgfortran/io/async.c b/libgfortran/io/async.c
index d216ace1947..247008ca801 100644
--- a/libgfortran/io/async.c
+++ b/libgfortran/io/async.c
@@ -117,13 +117,13 @@ async_io (void *arg)
{
case AIO_WRITE_DONE:
NOTE ("Finalizing write");
- st_write_done_worker (au->pdt);
+ st_write_done_worker (au->pdt, false);
UNLOCK (&au->io_lock);
break;
case AIO_READ_DONE:
NOTE ("Finalizing read");
- st_read_done_worker (au->pdt);
+ st_read_done_worker (au->pdt, false);
UNLOCK (&au->io_lock);
break;
diff --git a/libgfortran/io/io.h b/libgfortran/io/io.h
index e0007c6bfe5..3355bc2fd8d 100644
--- a/libgfortran/io/io.h
+++ b/libgfortran/io/io.h
@@ -1083,11 +1083,11 @@ default_precision_for_float (int kind)
#endif
extern void
-st_write_done_worker (st_parameter_dt *);
+st_write_done_worker (st_parameter_dt *, bool);
internal_proto (st_write_done_worker);
extern void
-st_read_done_worker (st_parameter_dt *);
+st_read_done_worker (st_parameter_dt *, bool);
internal_proto (st_read_done_worker);
extern void
diff --git a/libgfortran/io/transfer.c b/libgfortran/io/transfer.c
index 71a935652e3..36e35b48cd3 100644
--- a/libgfortran/io/transfer.c
+++ b/libgfortran/io/transfer.c
@@ -4337,7 +4337,7 @@ extern void st_read_done (st_parameter_dt *);
export_proto(st_read_done);
void
-st_read_done_worker (st_parameter_dt *dtp)
+st_read_done_worker (st_parameter_dt *dtp, bool unlock)
{
bool free_newunit = false;
finalize_transfer (dtp);
@@ -4367,7 +4367,8 @@ st_read_done_worker (st_parameter_dt *dtp)
free_format (dtp);
}
}
- unlock_unit (dtp->u.p.current_unit);
+ if (unlock)
+ unlock_unit (dtp->u.p.current_unit);
if (free_newunit)
{
/* Avoid inverse lock issues by placing after unlock_unit. */
@@ -4394,7 +4395,7 @@ st_read_done (st_parameter_dt *dtp)
unlock_unit (dtp->u.p.current_unit);
}
else
- st_read_done_worker (dtp); /* Calls unlock_unit. */
+ st_read_done_worker (dtp, true); /* Calls unlock_unit. */
}
library_end ();
@@ -4412,7 +4413,7 @@ st_write (st_parameter_dt *dtp)
void
-st_write_done_worker (st_parameter_dt *dtp)
+st_write_done_worker (st_parameter_dt *dtp, bool unlock)
{
bool free_newunit = false;
finalize_transfer (dtp);
@@ -4463,7 +4464,8 @@ st_write_done_worker (st_parameter_dt *dtp)
free_format (dtp);
}
}
- unlock_unit (dtp->u.p.current_unit);
+ if (unlock)
+ unlock_unit (dtp->u.p.current_unit);
if (free_newunit)
{
/* Avoid inverse lock issues by placing after unlock_unit. */
@@ -4496,7 +4498,7 @@ st_write_done (st_parameter_dt *dtp)
unlock_unit (dtp->u.p.current_unit);
}
else
- st_write_done_worker (dtp); /* Calls unlock_unit. */
+ st_write_done_worker (dtp, true); /* Calls unlock_unit. */
}
library_end ();
