[linux-2.6-block.git] / fs / ext4 / mmp.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/fs.h>
#include <linux/random.h>
#include <linux/buffer_head.h>
#include <linux/utsname.h>
#include <linux/kthread.h>

#include "ext4.h"

/* Checksumming functions */
static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	int offset = offsetof(struct mmp_struct, mmp_checksum);
	__u32 csum;

	csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);

	return cpu_to_le32(csum);
}

static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
{
	if (!ext4_has_metadata_csum(sb))
		return 1;

	return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
}

static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
{
	if (!ext4_has_metadata_csum(sb))
		return;

	mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
}

/*
 * Write the MMP block using REQ_SYNC to try to get the block on-disk
 * faster.
 */
static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
{
	struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);

	/*
	 * We protect against freezing so that we don't create dirty buffers
	 * on frozen filesystem.
	 */
	sb_start_write(sb);
	ext4_mmp_csum_set(sb, mmp);
	mark_buffer_dirty(bh);
	lock_buffer(bh);
	bh->b_end_io = end_buffer_write_sync;
	get_bh(bh);
	submit_bh(REQ_OP_WRITE, REQ_SYNC | REQ_META | REQ_PRIO, bh);
	wait_on_buffer(bh);
	sb_end_write(sb);
	if (unlikely(!buffer_uptodate(bh)))
		return 1;

	return 0;
}

/*
 * Read the MMP block. It _must_ be read from disk and hence we clear the
 * uptodate flag on the buffer.
 */
static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
			  ext4_fsblk_t mmp_block)
{
	struct mmp_struct *mmp;
	int ret;

	if (*bh)
		clear_buffer_uptodate(*bh);

	/* This would be sb_bread(sb, mmp_block), except we need to be sure
	 * that the MD RAID device cache has been bypassed, and that the read
	 * is not blocked in the elevator. */
	if (!*bh) {
		*bh = sb_getblk(sb, mmp_block);
		if (!*bh) {
			ret = -ENOMEM;
			goto warn_exit;
		}
	}

	get_bh(*bh);
	lock_buffer(*bh);
	(*bh)->b_end_io = end_buffer_read_sync;
	submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, *bh);
	wait_on_buffer(*bh);
	if (!buffer_uptodate(*bh)) {
		ret = -EIO;
		goto warn_exit;
	}
	mmp = (struct mmp_struct *)((*bh)->b_data);
	if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
		ret = -EFSCORRUPTED;
		goto warn_exit;
	}
	if (!ext4_mmp_csum_verify(sb, mmp)) {
		ret = -EFSBADCRC;
		goto warn_exit;
	}
	return 0;
warn_exit:
	brelse(*bh);
	*bh = NULL;
	ext4_warning(sb, "Error %d while reading MMP block %llu",
		     ret, mmp_block);
	return ret;
}

/*
 * Dump as much information as possible to help the admin.
 */
void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
		    const char *function, unsigned int line, const char *msg)
{
	__ext4_warning(sb, function, line, "%s", msg);
	__ext4_warning(sb, function, line,
		       "MMP failure info: last update time: %llu, last update "
		       "node: %s, last update device: %s",
		       (long long unsigned int) le64_to_cpu(mmp->mmp_time),
		       mmp->mmp_nodename, mmp->mmp_bdevname);
}

/*
 * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
 */
static int kmmpd(void *data)
{
	struct super_block *sb = ((struct mmpd_data *) data)->sb;
	struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
	struct mmp_struct *mmp;
	ext4_fsblk_t mmp_block;
	u32 seq = 0;
	unsigned long failed_writes = 0;
	int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
	unsigned mmp_check_interval;
	unsigned long last_update_time;
	unsigned long diff;
	int retval;

	mmp_block = le64_to_cpu(es->s_mmp_block);
	mmp = (struct mmp_struct *)(bh->b_data);
	mmp->mmp_time = cpu_to_le64(get_seconds());
	/*
	 * Start with the higher mmp_check_interval and reduce it if
	 * the MMP block is being updated on time.
	 */
	mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
				 EXT4_MMP_MIN_CHECK_INTERVAL);
	mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
	bdevname(bh->b_bdev, mmp->mmp_bdevname);

	memcpy(mmp->mmp_nodename, init_utsname()->nodename,
	       sizeof(mmp->mmp_nodename));

	while (!kthread_should_stop()) {
		if (++seq > EXT4_MMP_SEQ_MAX)
			seq = 1;

		mmp->mmp_seq = cpu_to_le32(seq);
		mmp->mmp_time = cpu_to_le64(get_seconds());
		last_update_time = jiffies;

		retval = write_mmp_block(sb, bh);
		/*
		 * Don't spew too many error messages. Print one every
		 * (s_mmp_update_interval * 60) seconds.
		 */
		if (retval) {
			if ((failed_writes % 60) == 0)
				ext4_error(sb, "Error writing to MMP block");
			failed_writes++;
		}

		if (!(le32_to_cpu(es->s_feature_incompat) &
		    EXT4_FEATURE_INCOMPAT_MMP)) {
			ext4_warning(sb, "kmmpd being stopped since MMP feature"
				     " has been disabled.");
			goto exit_thread;
		}

		if (sb_rdonly(sb)) {
			ext4_warning(sb, "kmmpd being stopped since filesystem "
				     "has been remounted as readonly.");
			goto exit_thread;
		}

		diff = jiffies - last_update_time;
		if (diff < mmp_update_interval * HZ)
			schedule_timeout_interruptible(mmp_update_interval *
						       HZ - diff);

		/*
		 * We need to make sure that more than mmp_check_interval
		 * seconds have not passed since writing. If that has happened
		 * we need to check if the MMP block is as we left it.
		 */
		diff = jiffies - last_update_time;
		if (diff > mmp_check_interval * HZ) {
			struct buffer_head *bh_check = NULL;
			struct mmp_struct *mmp_check;

			retval = read_mmp_block(sb, &bh_check, mmp_block);
			if (retval) {
				ext4_error(sb, "error reading MMP data: %d",
					   retval);
				goto exit_thread;
			}

			mmp_check = (struct mmp_struct *)(bh_check->b_data);
			if (mmp->mmp_seq != mmp_check->mmp_seq ||
			    memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
				   sizeof(mmp->mmp_nodename))) {
				dump_mmp_msg(sb, mmp_check,
					     "Error while updating MMP info. "
					     "The filesystem seems to have been"
					     " multiply mounted.");
				ext4_error(sb, "abort");
				put_bh(bh_check);
				retval = -EBUSY;
				goto exit_thread;
			}
			put_bh(bh_check);
		}

		 /*
		 * Adjust the mmp_check_interval depending on how much time
		 * it took for the MMP block to be written.
		 */
		mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
					     EXT4_MMP_MAX_CHECK_INTERVAL),
					 EXT4_MMP_MIN_CHECK_INTERVAL);
		mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
	}

	/*
	 * Unmount seems to be clean.
	 */
	mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
	mmp->mmp_time = cpu_to_le64(get_seconds());

	retval = write_mmp_block(sb, bh);

exit_thread:
	EXT4_SB(sb)->s_mmp_tsk = NULL;
	kfree(data);
	brelse(bh);
	return retval;
}

/*
 * Get a random new sequence number but make sure it is not greater than
 * EXT4_MMP_SEQ_MAX.
 */
static unsigned int mmp_new_seq(void)
{
	u32 new_seq;

	do {
		new_seq = prandom_u32();
	} while (new_seq > EXT4_MMP_SEQ_MAX);

	return new_seq;
}

/*
 * Protect the filesystem from being mounted more than once.
 */
int ext4_multi_mount_protect(struct super_block *sb,
				    ext4_fsblk_t mmp_block)
{
	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
	struct buffer_head *bh = NULL;
	struct mmp_struct *mmp = NULL;
	struct mmpd_data *mmpd_data;
	u32 seq;
	unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
	unsigned int wait_time = 0;
	int retval;

	if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
	    mmp_block >= ext4_blocks_count(es)) {
		ext4_warning(sb, "Invalid MMP block in superblock");
		goto failed;
	}

	retval = read_mmp_block(sb, &bh, mmp_block);
	if (retval)
		goto failed;

	mmp = (struct mmp_struct *)(bh->b_data);

	if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
		mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;

	/*
	 * If check_interval in MMP block is larger, use that instead of
	 * update_interval from the superblock.
	 */
	if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
		mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);

	seq = le32_to_cpu(mmp->mmp_seq);
	if (seq == EXT4_MMP_SEQ_CLEAN)
		goto skip;

	if (seq == EXT4_MMP_SEQ_FSCK) {
		dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
		goto failed;
	}

	wait_time = min(mmp_check_interval * 2 + 1,
			mmp_check_interval + 60);

	/* Print MMP interval if more than 20 secs. */
	if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
		ext4_warning(sb, "MMP interval %u higher than expected, please"
			     " wait.\n", wait_time * 2);

	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
		ext4_warning(sb, "MMP startup interrupted, failing mount\n");
		goto failed;
	}

	retval = read_mmp_block(sb, &bh, mmp_block);
	if (retval)
		goto failed;
	mmp = (struct mmp_struct *)(bh->b_data);
	if (seq != le32_to_cpu(mmp->mmp_seq)) {
		dump_mmp_msg(sb, mmp,
			     "Device is already active on another node.");
		goto failed;
	}

skip:
	/*
	 * write a new random sequence number.
	 */
	seq = mmp_new_seq();
	mmp->mmp_seq = cpu_to_le32(seq);

	retval = write_mmp_block(sb, bh);
	if (retval)
		goto failed;

	/*
	 * wait for MMP interval and check mmp_seq.
	 */
	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
		ext4_warning(sb, "MMP startup interrupted, failing mount");
		goto failed;
	}

	retval = read_mmp_block(sb, &bh, mmp_block);
	if (retval)
		goto failed;
	mmp = (struct mmp_struct *)(bh->b_data);
	if (seq != le32_to_cpu(mmp->mmp_seq)) {
		dump_mmp_msg(sb, mmp,
			     "Device is already active on another node.");
		goto failed;
	}

	mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
	if (!mmpd_data) {
		ext4_warning(sb, "not enough memory for mmpd_data");
		goto failed;
	}
	mmpd_data->sb = sb;
	mmpd_data->bh = bh;

	/*
	 * Start a kernel thread to update the MMP block periodically.
	 */
	EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
					     bdevname(bh->b_bdev,
						      mmp->mmp_bdevname));
	if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
		EXT4_SB(sb)->s_mmp_tsk = NULL;
		kfree(mmpd_data);
		ext4_warning(sb, "Unable to create kmmpd thread for %s.",
			     sb->s_id);
		goto failed;
	}

	return 0;

failed:
	brelse(bh);
	return 1;
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
c5e06d10 JL	2	#include <linux/fs.h>
	3	#include <linux/random.h>
	4	#include <linux/buffer_head.h>
	5	#include <linux/utsname.h>
	6	#include <linux/kthread.h>
	7
	8	#include "ext4.h"
	9
5c359a47	10	/* Checksumming functions */
171a7f21	11	static __le32 ext4_mmp_csum(struct super_block sb, struct mmp_struct mmp)
5c359a47 DW	12	{
	13	struct ext4_sb_info *sbi = EXT4_SB(sb);
	14	int offset = offsetof(struct mmp_struct, mmp_checksum);
	15	__u32 csum;
	16
	17	csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
	18
	19	return cpu_to_le32(csum);
	20	}
	21
c197855e	22	static int ext4_mmp_csum_verify(struct super_block sb, struct mmp_struct mmp)
5c359a47	23	{
9aa5d32b	24	if (!ext4_has_metadata_csum(sb))
5c359a47 DW	25	return 1;
	26
	27	return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
	28	}
	29
c197855e	30	static void ext4_mmp_csum_set(struct super_block sb, struct mmp_struct mmp)
5c359a47	31	{
9aa5d32b	32	if (!ext4_has_metadata_csum(sb))
5c359a47 DW	33	return;
	34
	35	mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
	36	}
	37
c5e06d10	38	/*
70fd7614	39	* Write the MMP block using REQ_SYNC to try to get the block on-disk
c5e06d10 JL	40	* faster.
c5e06d10 JL	41	*/
5c359a47	42	static int write_mmp_block(struct super_block sb, struct buffer_head bh)
c5e06d10	43	{
5c359a47 DW	44	struct mmp_struct mmp = (struct mmp_struct )(bh->b_data);
5c359a47 DW	45
8e8ad8a5 JK	46	/*
	47	* We protect against freezing so that we don't create dirty buffers
	48	* on frozen filesystem.
	49	*/
	50	sb_start_write(sb);
5c359a47	51	ext4_mmp_csum_set(sb, mmp);
c5e06d10 JL	52	mark_buffer_dirty(bh);
	53	lock_buffer(bh);
	54	bh->b_end_io = end_buffer_write_sync;
	55	get_bh(bh);
70fd7614	56	submit_bh(REQ_OP_WRITE, REQ_SYNC \| REQ_META \| REQ_PRIO, bh);
c5e06d10	57	wait_on_buffer(bh);
8e8ad8a5	58	sb_end_write(sb);
c5e06d10 JL	59	if (unlikely(!buffer_uptodate(bh)))
	60	return 1;
	61
	62	return 0;
	63	}
	64
	65	/*
	66	* Read the MMP block. It _must_ be read from disk and hence we clear the
	67	* uptodate flag on the buffer.
	68	*/
	69	static int read_mmp_block(struct super_block sb, struct buffer_head *bh,
	70	ext4_fsblk_t mmp_block)
	71	{
	72	struct mmp_struct *mmp;
98104468	73	int ret;
c5e06d10 JL	74
	75	if (*bh)
	76	clear_buffer_uptodate(*bh);
	77
	78	/* This would be sb_bread(sb, mmp_block), except we need to be sure
	79	* that the MD RAID device cache has been bypassed, and that the read
	80	* is not blocked in the elevator. */
98104468	81	if (!*bh) {
c5e06d10	82	*bh = sb_getblk(sb, mmp_block);
98104468 DC	83	if (!*bh) {
	84	ret = -ENOMEM;
	85	goto warn_exit;
c5e06d10 JL	86	}
c5e06d10 JL	87	}
98104468 DC	88
	89	get_bh(*bh);
	90	lock_buffer(*bh);
	91	(*bh)->b_end_io = end_buffer_read_sync;
70fd7614	92	submit_bh(REQ_OP_READ, REQ_META \| REQ_PRIO, *bh);
98104468 DC	93	wait_on_buffer(*bh);
98104468 DC	94	if (!buffer_uptodate(*bh)) {
98104468 DC	95	ret = -EIO;
98104468 DC	96	goto warn_exit;
c5e06d10	97	}
c5e06d10	98	mmp = (struct mmp_struct )((bh)->b_data);
03046886	99	if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
6a797d27	100	ret = -EFSCORRUPTED;
03046886	101	goto warn_exit;
	102	}
	103	if (!ext4_mmp_csum_verify(sb, mmp)) {
6a797d27	104	ret = -EFSBADCRC;
03046886	105	goto warn_exit;
	106	}
	107	return 0;
98104468	108	warn_exit:
03046886	109	brelse(*bh);
03046886	110	*bh = NULL;
98104468 DC	111	ext4_warning(sb, "Error %d while reading MMP block %llu",
	112	ret, mmp_block);
	113	return ret;
c5e06d10 JL	114	}
	115
	116	/*
	117	* Dump as much information as possible to help the admin.
	118	*/
	119	void __dump_mmp_msg(struct super_block sb, struct mmp_struct mmp,
	120	const char function, unsigned int line, const char msg)
	121	{
da0b5e40	122	__ext4_warning(sb, function, line, "%s", msg);
c5e06d10 JL	123	__ext4_warning(sb, function, line,
c5e06d10 JL	124	"MMP failure info: last update time: %llu, last update "
8d2ae1cb	125	"node: %s, last update device: %s",
c5e06d10 JL	126	(long long unsigned int) le64_to_cpu(mmp->mmp_time),
	127	mmp->mmp_nodename, mmp->mmp_bdevname);
	128	}
	129
	130	/*
	131	* kmmpd will update the MMP sequence every s_mmp_update_interval seconds
	132	*/
	133	static int kmmpd(void *data)
	134	{
	135	struct super_block sb = ((struct mmpd_data ) data)->sb;
	136	struct buffer_head bh = ((struct mmpd_data ) data)->bh;
	137	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
	138	struct mmp_struct *mmp;
	139	ext4_fsblk_t mmp_block;
	140	u32 seq = 0;
	141	unsigned long failed_writes = 0;
	142	int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
	143	unsigned mmp_check_interval;
	144	unsigned long last_update_time;
	145	unsigned long diff;
	146	int retval;
	147
	148	mmp_block = le64_to_cpu(es->s_mmp_block);
	149	mmp = (struct mmp_struct *)(bh->b_data);
	150	mmp->mmp_time = cpu_to_le64(get_seconds());
	151	/*
	152	* Start with the higher mmp_check_interval and reduce it if
	153	* the MMP block is being updated on time.
	154	*/
	155	mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
	156	EXT4_MMP_MIN_CHECK_INTERVAL);
	157	mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
	158	bdevname(bh->b_bdev, mmp->mmp_bdevname);
	159
215fc6af	160	memcpy(mmp->mmp_nodename, init_utsname()->nodename,
c5e06d10 JL	161	sizeof(mmp->mmp_nodename));
	162
	163	while (!kthread_should_stop()) {
	164	if (++seq > EXT4_MMP_SEQ_MAX)
	165	seq = 1;
	166
	167	mmp->mmp_seq = cpu_to_le32(seq);
	168	mmp->mmp_time = cpu_to_le64(get_seconds());
	169	last_update_time = jiffies;
	170
5c359a47	171	retval = write_mmp_block(sb, bh);
c5e06d10 JL	172	/*
	173	* Don't spew too many error messages. Print one every
	174	* (s_mmp_update_interval * 60) seconds.
	175	*/
bdfc230f NA	176	if (retval) {
	177	if ((failed_writes % 60) == 0)
	178	ext4_error(sb, "Error writing to MMP block");
c5e06d10 JL	179	failed_writes++;
	180	}
	181
	182	if (!(le32_to_cpu(es->s_feature_incompat) &
	183	EXT4_FEATURE_INCOMPAT_MMP)) {
	184	ext4_warning(sb, "kmmpd being stopped since MMP feature"
	185	" has been disabled.");
03046886	186	goto exit_thread;
c5e06d10 JL	187	}
c5e06d10 JL	188
bc98a42c	189	if (sb_rdonly(sb)) {
c5e06d10 JL	190	ext4_warning(sb, "kmmpd being stopped since filesystem "
c5e06d10 JL	191	"has been remounted as readonly.");
03046886	192	goto exit_thread;
c5e06d10 JL	193	}
	194
	195	diff = jiffies - last_update_time;
	196	if (diff < mmp_update_interval * HZ)
	197	schedule_timeout_interruptible(mmp_update_interval *
	198	HZ - diff);
	199
	200	/*
	201	* We need to make sure that more than mmp_check_interval
	202	* seconds have not passed since writing. If that has happened
	203	* we need to check if the MMP block is as we left it.
	204	*/
	205	diff = jiffies - last_update_time;
	206	if (diff > mmp_check_interval * HZ) {
	207	struct buffer_head *bh_check = NULL;
	208	struct mmp_struct *mmp_check;
	209
	210	retval = read_mmp_block(sb, &bh_check, mmp_block);
	211	if (retval) {
	212	ext4_error(sb, "error reading MMP data: %d",
	213	retval);
03046886	214	goto exit_thread;
c5e06d10 JL	215	}
	216
	217	mmp_check = (struct mmp_struct *)(bh_check->b_data);
	218	if (mmp->mmp_seq != mmp_check->mmp_seq \|\|
	219	memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
	220	sizeof(mmp->mmp_nodename))) {
	221	dump_mmp_msg(sb, mmp_check,
	222	"Error while updating MMP info. "
	223	"The filesystem seems to have been"
	224	" multiply mounted.");
	225	ext4_error(sb, "abort");
03046886	226	put_bh(bh_check);
	227	retval = -EBUSY;
	228	goto exit_thread;
c5e06d10 JL	229	}
	230	put_bh(bh_check);
	231	}
	232
	233	/*
	234	* Adjust the mmp_check_interval depending on how much time
	235	* it took for the MMP block to be written.
	236	*/
	237	mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
	238	EXT4_MMP_MAX_CHECK_INTERVAL),
	239	EXT4_MMP_MIN_CHECK_INTERVAL);
	240	mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
	241	}
	242
	243	/*
	244	* Unmount seems to be clean.
	245	*/
	246	mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
	247	mmp->mmp_time = cpu_to_le64(get_seconds());
	248
5c359a47	249	retval = write_mmp_block(sb, bh);
c5e06d10	250
03046886	251	exit_thread:
03046886	252	EXT4_SB(sb)->s_mmp_tsk = NULL;
c5e06d10 JL	253	kfree(data);
	254	brelse(bh);
	255	return retval;
	256	}
	257
	258	/*
	259	* Get a random new sequence number but make sure it is not greater than
	260	* EXT4_MMP_SEQ_MAX.
	261	*/
	262	static unsigned int mmp_new_seq(void)
	263	{
	264	u32 new_seq;
	265
	266	do {
dd1f723b	267	new_seq = prandom_u32();
c5e06d10 JL	268	} while (new_seq > EXT4_MMP_SEQ_MAX);
	269
	270	return new_seq;
	271	}
	272
	273	/*
	274	* Protect the filesystem from being mounted more than once.
	275	*/
	276	int ext4_multi_mount_protect(struct super_block *sb,
	277	ext4_fsblk_t mmp_block)
	278	{
	279	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
	280	struct buffer_head *bh = NULL;
	281	struct mmp_struct *mmp = NULL;
	282	struct mmpd_data *mmpd_data;
	283	u32 seq;
	284	unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
	285	unsigned int wait_time = 0;
	286	int retval;
	287
	288	if (mmp_block < le32_to_cpu(es->s_first_data_block) \|\|
	289	mmp_block >= ext4_blocks_count(es)) {
	290	ext4_warning(sb, "Invalid MMP block in superblock");
	291	goto failed;
	292	}
	293
	294	retval = read_mmp_block(sb, &bh, mmp_block);
	295	if (retval)
	296	goto failed;
	297
	298	mmp = (struct mmp_struct *)(bh->b_data);
	299
	300	if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
	301	mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
	302
	303	/*
	304	* If check_interval in MMP block is larger, use that instead of
	305	* update_interval from the superblock.
	306	*/
85d21650 SN	307	if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
85d21650 SN	308	mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
c5e06d10 JL	309
	310	seq = le32_to_cpu(mmp->mmp_seq);
	311	if (seq == EXT4_MMP_SEQ_CLEAN)
	312	goto skip;
	313
	314	if (seq == EXT4_MMP_SEQ_FSCK) {
	315	dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
	316	goto failed;
	317	}
	318
	319	wait_time = min(mmp_check_interval * 2 + 1,
	320	mmp_check_interval + 60);
	321
	322	/* Print MMP interval if more than 20 secs. */
	323	if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
	324	ext4_warning(sb, "MMP interval %u higher than expected, please"
	325	" wait.\n", wait_time * 2);
	326
	327	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
	328	ext4_warning(sb, "MMP startup interrupted, failing mount\n");
	329	goto failed;
	330	}
	331
	332	retval = read_mmp_block(sb, &bh, mmp_block);
	333	if (retval)
	334	goto failed;
	335	mmp = (struct mmp_struct *)(bh->b_data);
	336	if (seq != le32_to_cpu(mmp->mmp_seq)) {
	337	dump_mmp_msg(sb, mmp,
	338	"Device is already active on another node.");
	339	goto failed;
	340	}
	341
	342	skip:
	343	/*
	344	* write a new random sequence number.
	345	*/
f6f96fdb DW	346	seq = mmp_new_seq();
f6f96fdb DW	347	mmp->mmp_seq = cpu_to_le32(seq);
c5e06d10	348
5c359a47	349	retval = write_mmp_block(sb, bh);
c5e06d10 JL	350	if (retval)
	351	goto failed;
	352
	353	/*
	354	* wait for MMP interval and check mmp_seq.
	355	*/
	356	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
8d2ae1cb	357	ext4_warning(sb, "MMP startup interrupted, failing mount");
c5e06d10 JL	358	goto failed;
	359	}
	360
	361	retval = read_mmp_block(sb, &bh, mmp_block);
	362	if (retval)
	363	goto failed;
	364	mmp = (struct mmp_struct *)(bh->b_data);
	365	if (seq != le32_to_cpu(mmp->mmp_seq)) {
	366	dump_mmp_msg(sb, mmp,
	367	"Device is already active on another node.");
	368	goto failed;
	369	}
	370
d695a1be	371	mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
c5e06d10 JL	372	if (!mmpd_data) {
	373	ext4_warning(sb, "not enough memory for mmpd_data");
	374	goto failed;
	375	}
	376	mmpd_data->sb = sb;
	377	mmpd_data->bh = bh;
	378
	379	/*
	380	* Start a kernel thread to update the MMP block periodically.
	381	*/
	382	EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
	383	bdevname(bh->b_bdev,
	384	mmp->mmp_bdevname));
	385	if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
	386	EXT4_SB(sb)->s_mmp_tsk = NULL;
	387	kfree(mmpd_data);
	388	ext4_warning(sb, "Unable to create kmmpd thread for %s.",
	389	sb->s_id);
	390	goto failed;
	391	}
	392
	393	return 0;
	394
	395	failed:
	396	brelse(bh);
	397	return 1;
	398	}
	399
	400