linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jan Kara <jack@suse.cz>
To: <linux-fsdevel@vger.kernel.org>
Cc: <linux-ext4@vger.kernel.org>, <linux-block@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>, yebin <yebin10@huawei.com>,
	Andreas Dilger <adilger@dilger.ca>, Jens Axboe <axboe@kernel.dk>,
	Jan Kara <jack@suse.cz>
Subject: [PATCH 2/2] block: Do not discard buffers under a mounted filesystem
Date: Fri,  4 Sep 2020 10:58:52 +0200	[thread overview]
Message-ID: <20200904085852.5639-3-jack@suse.cz> (raw)
In-Reply-To: <20200904085852.5639-1-jack@suse.cz>

Discarding blocks and buffers under a mounted filesystem is hardly
anything admin wants to do. Usually it will confuse the filesystem and
sometimes the loss of buffer_head state (including b_private field) can
even cause crashes like:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
PGD 0 P4D 0
Oops: 0002 [#1] SMP PTI
CPU: 4 PID: 203778 Comm: jbd2/dm-3-8 Kdump: loaded Tainted: G O     --------- -  - 4.18.0-147.5.0.5.h126.eulerosv2r9.x86_64 #1
Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 1.57 08/11/2015
RIP: 0010:jbd2_journal_grab_journal_head+0x1b/0x40 [jbd2]
...
Call Trace:
 __jbd2_journal_insert_checkpoint+0x23/0x70 [jbd2]
 jbd2_journal_commit_transaction+0x155f/0x1b60 [jbd2]
 kjournald2+0xbd/0x270 [jbd2]

So if we don't have block device open with O_EXCL already, claim the
block device while we truncate buffer cache. This makes sure any
exclusive block device user (such as filesystem) cannot operate on the
device while we are discarding buffer cache.

Reported-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/ioctl.c          | 16 ++++++++++------
 fs/block_dev.c         | 37 +++++++++++++++++++++++++++++++++----
 include/linux/blkdev.h |  7 +++++++
 3 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index bdb3bbb253d9..ae74d0409afa 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -112,8 +112,7 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
 	uint64_t range[2];
 	uint64_t start, len;
 	struct request_queue *q = bdev_get_queue(bdev);
-	struct address_space *mapping = bdev->bd_inode->i_mapping;
-
+	int err;
 
 	if (!(mode & FMODE_WRITE))
 		return -EBADF;
@@ -134,7 +133,11 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
 
 	if (start + len > i_size_read(bdev->bd_inode))
 		return -EINVAL;
-	truncate_inode_pages_range(mapping, start, start + len - 1);
+
+	err = truncate_bdev_range(bdev, mode, start, start + len - 1);
+	if (err)
+		return err;
+
 	return blkdev_issue_discard(bdev, start >> 9, len >> 9,
 				    GFP_KERNEL, flags);
 }
@@ -143,8 +146,8 @@ static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
 		unsigned long arg)
 {
 	uint64_t range[2];
-	struct address_space *mapping;
 	uint64_t start, end, len;
+	int err;
 
 	if (!(mode & FMODE_WRITE))
 		return -EBADF;
@@ -166,8 +169,9 @@ static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
 		return -EINVAL;
 
 	/* Invalidate the page cache, including dirty pages */
-	mapping = bdev->bd_inode->i_mapping;
-	truncate_inode_pages_range(mapping, start, end);
+	err = truncate_bdev_range(bdev, mode, start, end);
+	if (err)
+		return err;
 
 	return blkdev_issue_zeroout(bdev, start >> 9, len >> 9, GFP_KERNEL,
 			BLKDEV_ZERO_NOUNMAP);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 8ae833e00443..02a749370717 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -103,6 +103,35 @@ void invalidate_bdev(struct block_device *bdev)
 }
 EXPORT_SYMBOL(invalidate_bdev);
 
+/*
+ * Drop all buffers & page cache for given bdev range. This function bails
+ * with error if bdev has other exclusive owner (such as filesystem).
+ */
+int truncate_bdev_range(struct block_device *bdev, fmode_t mode,
+			loff_t lstart, loff_t lend)
+{
+	struct block_device *claimed_bdev = NULL;
+	int err;
+
+	/*
+	 * If we don't hold exclusive handle for the device, upgrade to it
+	 * while we discard the buffer cache to avoid discarding buffers
+	 * under live filesystem.
+	 */
+	if (!(mode & FMODE_EXCL)) {
+		claimed_bdev = bdev->bd_contains;
+		err = bd_prepare_to_claim(bdev, claimed_bdev,
+					  truncate_bdev_range);
+		if (err)
+			return err;
+	}
+	truncate_inode_pages_range(bdev->bd_inode->i_mapping, lstart, lend);
+	if (claimed_bdev)
+		bd_abort_claiming(bdev, claimed_bdev, truncate_bdev_range);
+	return 0;
+}
+EXPORT_SYMBOL(truncate_bdev_range);
+
 static void set_init_blocksize(struct block_device *bdev)
 {
 	bdev->bd_inode->i_blkbits = blksize_bits(bdev_logical_block_size(bdev));
@@ -1969,7 +1998,6 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 			     loff_t len)
 {
 	struct block_device *bdev = I_BDEV(bdev_file_inode(file));
-	struct address_space *mapping;
 	loff_t end = start + len - 1;
 	loff_t isize;
 	int error;
@@ -1997,8 +2025,9 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 		return -EINVAL;
 
 	/* Invalidate the page cache, including dirty pages. */
-	mapping = bdev->bd_inode->i_mapping;
-	truncate_inode_pages_range(mapping, start, end);
+	error = truncate_bdev_range(bdev, file->f_mode, start, end);
+	if (error)
+		return error;
 
 	switch (mode) {
 	case FALLOC_FL_ZERO_RANGE:
@@ -2025,7 +2054,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	 * the caller will be given -EBUSY.  The third argument is
 	 * inclusive, so the rounding here is safe.
 	 */
-	return invalidate_inode_pages2_range(mapping,
+	return invalidate_inode_pages2_range(bdev->bd_inode->i_mapping,
 					     start >> PAGE_SHIFT,
 					     end >> PAGE_SHIFT);
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index bb5636cc17b9..91c62bfb2042 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1984,11 +1984,18 @@ void bdput(struct block_device *);
 
 #ifdef CONFIG_BLOCK
 void invalidate_bdev(struct block_device *bdev);
+int truncate_bdev_range(struct block_device *bdev, fmode_t mode, loff_t lstart,
+			loff_t lend);
 int sync_blockdev(struct block_device *bdev);
 #else
 static inline void invalidate_bdev(struct block_device *bdev)
 {
 }
+int truncate_bdev_range(struct block_device *bdev, fmode_t mode, loff_t lstart,
+			loff_t lend)
+{
+	return 0;
+}
 static inline int sync_blockdev(struct block_device *bdev)
 {
 	return 0;
-- 
2.16.4


  parent reply	other threads:[~2020-09-04  8:59 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04  8:58 [PATCH 0/2 v2] bdev: Avoid discarding buffers under a filesystem Jan Kara
2020-09-04  8:58 ` [PATCH 1/2] fs: Don't invalidate page buffers in block_write_full_page() Jan Kara
2020-09-07  7:12   ` Christoph Hellwig
2020-09-04  8:58 ` Jan Kara [this message]
2020-09-07  7:12   ` [PATCH 2/2] block: Do not discard buffers under a mounted filesystem Christoph Hellwig
2020-09-07 10:35 ` [PATCH 0/2 v2] bdev: Avoid discarding buffers under a filesystem Jan Kara
2020-09-07 16:24   ` Jens Axboe

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200904085852.5639-3-jack@suse.cz \
    --to=jack@suse.cz \
    --cc=adilger@dilger.ca \
    --cc=axboe@kernel.dk \
    --cc=hch@infradead.org \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-ext4@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=yebin10@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).