Patch "loop: Disable fallocate() zero and discard if not supported" has been added to the 6.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    loop: Disable fallocate() zero and discard if not supported

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     loop-disable-fallocate-zero-and-discard-if-not-suppo.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6718aa792b7d297ece53024a138ea679e8153ea6
Author: Cyril Hrubis <chrubis@xxxxxxx>
Date:   Thu Jun 13 18:38:17 2024 +0200

    loop: Disable fallocate() zero and discard if not supported
    
    [ Upstream commit 5f75e081ab5cbfbe7aca2112a802e69576ee9778 ]
    
    If fallcate is implemented but zero and discard operations are not
    supported by the filesystem the backing file is on we continue to fill
    dmesg with errors from the blk_mq_end_request() since each time we call
    fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
    ends up propagated into the block layer. In the end syscall succeeds
    since the blkdev_issue_zeroout() falls back to writing zeroes which
    makes the errors even more misleading and confusing.
    
    How to reproduce:
    
    1. make sure /tmp is mounted as tmpfs
    2. dd if=/dev/zero of=/tmp/disk.img bs=1M count=100
    3. losetup /dev/loop0 /tmp/disk.img
    4. mkfs.ext2 /dev/loop0
    5. dmesg |tail
    
    [710690.898214] operation not supported error, dev loop0, sector 204672 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898279] operation not supported error, dev loop0, sector 522 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898603] operation not supported error, dev loop0, sector 16906 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898917] operation not supported error, dev loop0, sector 32774 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899218] operation not supported error, dev loop0, sector 49674 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899484] operation not supported error, dev loop0, sector 65542 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899743] operation not supported error, dev loop0, sector 82442 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900015] operation not supported error, dev loop0, sector 98310 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900276] operation not supported error, dev loop0, sector 115210 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900546] operation not supported error, dev loop0, sector 131078 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    
    This patch changes the lo_fallocate() to clear the flags for zero and
    discard operations if we get EOPNOTSUPP from the backing file fallocate
    callback, that way we at least stop spewing errors after the first
    unsuccessful try.
    
    CC: Jan Kara <jack@xxxxxxx>
    Signed-off-by: Cyril Hrubis <chrubis@xxxxxxx>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Reviewed-by: Jan Kara <jack@xxxxxxx>
    Link: https://lore.kernel.org/r/20240613163817.22640-1-chrubis@xxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 28a95fd366fea..95a468eaa7013 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -302,6 +302,21 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
 	return 0;
 }
 
+static void loop_clear_limits(struct loop_device *lo, int mode)
+{
+	struct queue_limits lim = queue_limits_start_update(lo->lo_queue);
+
+	if (mode & FALLOC_FL_ZERO_RANGE)
+		lim.max_write_zeroes_sectors = 0;
+
+	if (mode & FALLOC_FL_PUNCH_HOLE) {
+		lim.max_hw_discard_sectors = 0;
+		lim.discard_granularity = 0;
+	}
+
+	queue_limits_commit_update(lo->lo_queue, &lim);
+}
+
 static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 			int mode)
 {
@@ -320,6 +335,14 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
 	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
 		return -EIO;
+
+	/*
+	 * We initially configure the limits in a hope that fallocate is
+	 * supported and clear them here if that turns out not to be true.
+	 */
+	if (unlikely(ret == -EOPNOTSUPP))
+		loop_clear_limits(lo, mode);
+
 	return ret;
 }