[PATCH 2/2] scsi_debug: fix module removal loop

Darrick J. Wong
2021-08-17T23:53:12Z

From: Darrick J. Wong <djwong@kernel.org>

Luis' recent patch changing the "sleep 1" to a "udevadm settle"
invocation exposed some race conditions in _put_scsi_debug_dev that
caused regressions in generic/108 on my machine. Looking at tracing
data, it looks like the udisks daemon will try to open the device at
some point after the filesystem unmounts; if this coincides with the
final 'rmmod scsi_debug', the test fails.

Examining the function, it is odd to me that the loop condition is
predicated only on whether or not modprobe /thinks/ it can remove the
module. Why not actually try (twice) actually to remove the module,
and then complain if a third attempt fails?

Also switch the final removal attempt to modprobe -r, since it returns
zero if the module isn't loaded.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
common/scsi_debug | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/common/scsi_debug b/common/scsi_debug
index e7988469..abaf6798 100644
--- a/common/scsi_debug
+++ b/common/scsi_debug
@@ -49,9 +49,9 @@ _put_scsi_debug_dev()
# use redirection not -q option of modprobe here, because -q of old
# modprobe is only quiet when the module is not found, not when the
# module is in use.
- while [ $n -ge 0 ] && ! modprobe -nr scsi_debug >/dev/null 2>&1; do
+ while [ $n -ge 0 ] && ! modprobe -r scsi_debug >/dev/null 2>&1; do
$UDEV_SETTLE_PROG
n=$((n-1))
done
- rmmod scsi_debug || _fail "Could not remove scsi_debug module"
+ modprobe -r scsi_debug || _fail "Could not remove scsi_debug module"
}