diff mbox series

[2/2] scsi_debug: fix module removal loop

Message ID 162924439095.779373.7171773658755331729.stgit@magnolia (mailing list archive)
State New, archived
Headers show
Series fstests: random fixes | expand

Commit Message

Darrick J. Wong Aug. 17, 2021, 11:53 p.m. UTC
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(-)

Comments

Zorro Lang Aug. 18, 2021, 3:55 a.m. UTC | #1
On Tue, Aug 17, 2021 at 04:53:10PM -0700, Darrick J. Wong wrote:
> 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"

Make sense, I don't understand why we need "dry-run" modprobe at here either.

Reviewed-by: Zorro Lang <zlang@redhat.com>

>  }
>
Eryu Guan Aug. 22, 2021, 12:19 p.m. UTC | #2
On Tue, Aug 17, 2021 at 04:53:10PM -0700, Darrick J. Wong wrote:
> 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))

Luis' new patch removed this while loop completely, and

>  	done
> -	rmmod scsi_debug || _fail "Could not remove scsi_debug module"
> +	modprobe -r scsi_debug || _fail "Could not remove scsi_debug module"

Replaced this rmmod with _patient_rmmod helper, which uses modprobe -r
to remove mod internally.

So I'd drop this patch. Thanks for the fix anyway!

Eryu
diff mbox series

Patch

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"
 }