[LTP] [PATCH V2] detach_device: Wait until the kernel frees the loop device

[LTP] [PATCH V2] detach_device: Wait until the kernel frees the loop device

[Stanislav Kholmanskikh]

On systems employing the "lazy loop device removal",
commit a1ecac3b0656 ("loop: Make explicit loop device destruction lazy"),
ioctl(LOOP_CLR_FD) may return 0 when the loop device is in use,
for example by udev.

Therefore, there is a chance that a quick attach/detach may not
give udev enough time to complete, like this:

open("file.img", O_RDWR)           = 4
ioctl(3, LOOP_SET_FD, 0x4)         = 0
close(3)                           = 0
close(4)                           = 0
open("/dev/loop0", O_RDONLY)       = 3
ioctl(3, LOOP_CLR_FD, 0)           = 0
close(3)                           = 0
open("/dev/loop0", O_RDWR)         = 3
open("file.img", O_RDWR)           = 4
ioctl(3, LOOP_SET_FD, 0x4)         = -1 EBUSY (Device or resource busy)

So let's wait until the kernel frees the loop device, i.e.
when ioctl(LOOP_CLR_FD) starts failing with ENXIO.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
---
 lib/tst_device.c |   22 ++++++++++++----------
 1 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/lib/tst_device.c b/lib/tst_device.c
index 3bded53..4725570 100644
--- a/lib/tst_device.c
+++ b/lib/tst_device.c
@@ -150,30 +150,32 @@ static void attach_device(void (*cleanup_fn)(void),
 
 static void detach_device(void (*cleanup_fn)(void), const char *dev)
 {
-	int dev_fd, err, i;
+	int dev_fd, ret, i;
 
 	dev_fd = SAFE_OPEN(cleanup_fn, dev, O_RDONLY);
 
-	/* keep trying to clear LOOPDEV fd if EBUSY, a quick succession
+	/* keep trying to clear LOOPDEV until we get ENXIO, a quick succession
 	 * of attach/detach might not give udev enough time to complete */
 	for (i = 0; i < 40; i++) {
-		if (ioctl(dev_fd, LOOP_CLR_FD, 0) == 0) {
+		ret = ioctl(dev_fd, LOOP_CLR_FD, 0);
+
+		if (ret && (errno == ENXIO)) {
 			close(dev_fd);
 			return;
 		}
-		if (errno != EBUSY) {
-			err = errno;
-			close(dev_fd);
-			tst_brkm(TBROK, cleanup_fn,
-				"ioctl(%s, LOOP_CLR_FD, 0) failed: %s",
-				dev, tst_strerrno(err));
+
+		if (ret && (errno != EBUSY)) {
+			tst_resm(TWARN,
+				 "ioctl(%s, LOOP_CLR_FD, 0) unexpectedly failed with: %s",
+				 dev, tst_strerrno(errno));
 		}
+
 		usleep(50000);
 	}
 
 	close(dev_fd);
 	tst_brkm(TBROK, cleanup_fn,
-		"ioctl(%s, LOOP_CLR_FD, 0) EBUSY for too long",	dev);
+		"ioctl(%s, LOOP_CLR_FD, 0) no ENXIO for too long", dev);
 }
 
 const char *tst_acquire_device(void (cleanup_fn)(void))
-- 
1.7.1


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Re: [LTP] [PATCH V2] detach_device: Wait until the kernel frees the loop device

[Cyril Hrubis]

Hi!
Acked.

-- 
Cyril Hrubis
chrubis@suse.cz

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