From: Bart Van Assche <bvanassche@acm.org>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] loop: avoid EAGAIN, if offset or block_size are changed
Date: Mon, 25 Nov 2019 10:35:54 -0800 [thread overview]
Message-ID: <a4e5d6bd-3685-379a-c388-cd2871827b21@acm.org> (raw)
In-Reply-To: <20191125175913.GC71634@jaegeuk-macbookpro.roam.corp.google.com>
On 11/25/19 9:59 AM, Jaegeuk Kim wrote:
> On 11/19, Bart Van Assche wrote:
>> On 5/17/19 5:53 PM, Jaegeuk Kim wrote:
>>> This patch tries to avoid EAGAIN due to nrpages!=0 that was originally trying
>>> to drop stale pages resulting in wrong data access.
>>>
>>> Report: https://bugs.chromium.org/p/chromium/issues/detail?id=938958#c38
>>
>> Please provide a more detailed commit description. What is wrong with the
>> current implementation and why is the new behavior considered the correct
>> behavior?
>
> Some history would be:
>
> Original bug fix is:
> commit 5db470e229e2 ("loop: drop caches if offset or block_size are changed"),
> which returns EAGAIN so that user land like Chrome would require enhancing their
> error handling routines.
>
> So, this patch tries to avoid EAGAIN while addressing the original bug.
>
>>
>> This patch moves draining code from before the following comment to after
>> that comment:
>>
>> /* I/O need to be drained during transfer transition */
>>
>> Is that comment still correct or should it perhaps be updated?
>
> IMHO, it's still valid.
Hi Jaegeuk,
Thank you for the additional and very helpful clarification. Can you have a look at the (totally untested) patch below? I prefer that version because it prevents concurrent processing of requests and syncing/killing the bdev.
Thanks,
Bart.
Subject: [PATCH] loop: Avoid EAGAIN if offset or block_size are changed
After sync_blockdev() and kill_bdev() have been called, more requests
can be submitted to the loop device. These requests dirty additional
pages, causing loop_set_status() to return -EAGAIN. Not all user space
code that changes the offset and/or the block size handles -EAGAIN
correctly. Hence make sure that loop_set_status() does not return
-EAGAIN.
Fixes: 5db470e229e2 ("loop: drop caches if offset or block_size are changed")
Reported-by: Gwendal Grignou <gwendal@chromium.org>
Reported-by: grygorii tertychnyi <gtertych@cisco.com>
Reported-by: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
drivers/block/loop.c | 35 +++++++----------------------------
1 file changed, 7 insertions(+), 28 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 739b372a5112..48cfc8b9c247 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1264,15 +1264,15 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
goto out_unlock;
}
+ /* I/O need to be drained during transfer transition */
+ blk_mq_freeze_queue(lo->lo_queue);
+
if (lo->lo_offset != info->lo_offset ||
lo->lo_sizelimit != info->lo_sizelimit) {
sync_blockdev(lo->lo_device);
kill_bdev(lo->lo_device);
}
- /* I/O need to be drained during transfer transition */
- blk_mq_freeze_queue(lo->lo_queue);
-
err = loop_release_xfer(lo);
if (err)
goto out_unfreeze;
@@ -1298,14 +1298,6 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
if (lo->lo_offset != info->lo_offset ||
lo->lo_sizelimit != info->lo_sizelimit) {
- /* kill_bdev should have truncated all the pages */
- if (lo->lo_device->bd_inode->i_mapping->nrpages) {
- err = -EAGAIN;
- pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
- __func__, lo->lo_number, lo->lo_file_name,
- lo->lo_device->bd_inode->i_mapping->nrpages);
- goto out_unfreeze;
- }
if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
err = -EFBIG;
goto out_unfreeze;
@@ -1531,39 +1523,26 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg)
static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
{
- int err = 0;
-
if (lo->lo_state != Lo_bound)
return -ENXIO;
if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
return -EINVAL;
+ blk_mq_freeze_queue(lo->lo_queue);
+
if (lo->lo_queue->limits.logical_block_size != arg) {
sync_blockdev(lo->lo_device);
kill_bdev(lo->lo_device);
}
-
- blk_mq_freeze_queue(lo->lo_queue);
-
- /* kill_bdev should have truncated all the pages */
- if (lo->lo_queue->limits.logical_block_size != arg &&
- lo->lo_device->bd_inode->i_mapping->nrpages) {
- err = -EAGAIN;
- pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
- __func__, lo->lo_number, lo->lo_file_name,
- lo->lo_device->bd_inode->i_mapping->nrpages);
- goto out_unfreeze;
- }
-
blk_queue_logical_block_size(lo->lo_queue, arg);
blk_queue_physical_block_size(lo->lo_queue, arg);
blk_queue_io_min(lo->lo_queue, arg);
loop_update_dio(lo);
-out_unfreeze:
+
blk_mq_unfreeze_queue(lo->lo_queue);
- return err;
+ return 0;
}
static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,
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next prev parent reply other threads:[~2019-11-25 18:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-18 0:47 [PATCH] loop: avoid EAGAIN, if offset or block_size are changed Jaegeuk Kim
2019-05-18 0:53 ` [PATCH v2] " Jaegeuk Kim
2019-06-17 21:08 ` [f2fs-dev] " Jaegeuk Kim
2019-11-18 18:36 ` [f2fs-dev] " Andrew Norrie
2019-11-19 4:00 ` Greg KH
2019-11-19 23:40 ` [f2fs-dev] [PATCH v2] " Bart Van Assche
2019-11-25 17:59 ` Jaegeuk Kim
2019-11-25 18:35 ` Bart Van Assche [this message]
2019-11-25 19:22 ` Jaegeuk Kim
2019-11-25 19:41 ` Bart Van Assche
2019-11-27 18:18 ` [f2fs-dev] [PATCH v3] " Jaegeuk Kim
2019-11-27 18:54 ` Bart Van Assche
2020-02-19 19:58 ` Andrew Norrie
2020-03-05 21:04 ` [f2fs-dev] [PATCH] " Jan Kara
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