linux-ext4 - [PATCH 14/16] fuse2fs: work around EBUSY discard returns from dm-thinp

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Message-ID: <176062915719.3343688.5400835821262447159.stgit@frogsfrogsfrogs>
Date: Thu, 16 Oct 2025 08:43:27 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH 14/16] fuse2fs: work around EBUSY discard returns from
 dm-thinp

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

generic/500 has this interesting failure mode when fuse2fs is running in
fuseblk mode:

 --- /run/fstests/bin/tests/generic/500.out      2025-07-15 14:45:15.092576090 -0700
 +++ /var/tmp/fstests/generic/500.out.bad        2025-09-05 15:09:35.211499883 -0700
 @@ -1,2 +1,22 @@
  QA output created by 500
 +fstrim: /opt: FITRIM ioctl failed: Device or resource busy

Apparently you can overwhelm dm-thinp with a large number of discard
requests, at which point it starts returning EBUSY.  This is unexpected
behavior but let's mask that off because discard is advisory anyways.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index b8db298cde202f..6864466435abfb 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -4038,6 +4038,14 @@ static int ioctl_fitrim(struct fuse2fs *ff, struct fuse2fs_file_handle *fh,

 		if (b - start >= minlen) {
 			err = io_channel_discard(fs->io, start, b - start);
+			if (err == EBUSY) {
+				/*
+				 * Apparently dm-thinp can return EBUSY when
+				 * it's too busy deallocating thinp units to
+				 * deallocate more.  Swallow these errors.
+				 */
+				err = 0;
+			}
 			if (err)
 				return translate_error(fs, fh->ino, err);
 			cleared += b - start;