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From: Matteo Croce <mcroce@linux.microsoft.com>
To: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
	"Lennart Poettering" <lennart@poettering.net>,
	"Luca Boccassi" <bluca@debian.org>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Damien Le Moal" <damien.lemoal@wdc.com>,
	"Tejun Heo" <tj@kernel.org>,
	"Javier González" <javier@javigon.com>,
	"Niklas Cassel" <niklas.cassel@wdc.com>,
	"Johannes Thumshirn" <johannes.thumshirn@wdc.com>,
	"Hannes Reinecke" <hare@suse.de>
Subject: [PATCH -next 5/5] loop: increment sequence number
Date: Mon, 15 Mar 2021 21:02:42 +0100
Message-ID: <20210315200242.67355-6-mcroce@linux.microsoft.com> (raw)
In-Reply-To: <20210315200242.67355-1-mcroce@linux.microsoft.com>

From: Matteo Croce <mcroce@microsoft.com>

On a very loaded system, if there are many events queued up from multiple
attach/detach cycles, it's impossible to match them up with the
LOOP_CONFIGURE or LOOP_SET_FD call, since we don't know where the position
of our own association in the queue is[1].
Not even an empty uevent queue is a reliable indication that we already
received the uevent we were waiting for, since with multi-partition block
devices each partition's event is queued asynchronously and might be
delivered later.

Increment the disk sequence number when setting or changing the backing
file, so the userspace knows which backing file generated the event.

[1] https://github.com/systemd/systemd/issues/17469#issuecomment-762919781

Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
 drivers/block/loop.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a370cde3ddd4..1541ccff81f9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -734,6 +734,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 		goto out_err;
 
 	/* and ... switch */
+	inc_diskseq(lo->lo_disk);
 	blk_mq_freeze_queue(lo->lo_queue);
 	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
 	lo->lo_backing_file = file;
@@ -1122,6 +1123,8 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	if (error)
 		goto out_unlock;
 
+	inc_diskseq(lo->lo_disk);
+
 	if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) ||
 	    !file->f_op->write_iter)
 		lo->lo_flags |= LO_FLAGS_READ_ONLY;
-- 
2.30.2


      parent reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15 20:02 [PATCH -next 0/5] block: add a sequence number to disks Matteo Croce
2021-03-15 20:02 ` [PATCH -next 1/5] block: add disk sequence number Matteo Croce
2021-03-15 20:18   ` Matthew Wilcox
2021-03-15 21:04     ` Matthew Wilcox
2021-03-15 21:32       ` Lennart Poettering
2021-03-25 17:29       ` Matteo Croce
2021-03-26  8:00         ` Hannes Reinecke
2021-03-25 20:58       ` Lennart Poettering
2021-03-16 14:13     ` Christoph Hellwig
2021-04-20 20:12       ` Lennart Poettering
2021-03-25 20:52     ` Lennart Poettering
2021-03-16  1:44   ` JeffleXu
2021-03-23 17:43     ` Matteo Croce
2021-03-15 20:02 ` [PATCH -next 2/5] block: add ioctl to read the " Matteo Croce
2021-03-15 20:13   ` Matthew Wilcox
2021-03-15 20:17     ` Damien Le Moal
2021-03-15 20:34     ` Matteo Croce
2021-03-15 20:02 ` [PATCH -next 3/5] block: refactor sysfs code Matteo Croce
2021-03-15 20:02 ` [PATCH -next 4/5] block: export diskseq in sysfs Matteo Croce
2021-03-15 20:02 ` Matteo Croce [this message]

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