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![Jan Kara](/assets/img/avatar_default.png)
The multi-mount protection kthread checks for read-only filesystem and aborts in that case. The remount code actually handles stopping of the kthread on remount so the only purpose of the check is in case of emergency remount read-only. Replace the check for read-only filesystem with a check for shutdown filesystem as running MMP on such is risky anyway and it makes ordering of things during remount simpler. Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20230616165109.21695-11-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
408 lines
10 KiB
C
408 lines
10 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/fs.h>
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#include <linux/random.h>
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#include <linux/buffer_head.h>
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#include <linux/utsname.h>
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#include <linux/kthread.h>
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#include "ext4.h"
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/* Checksumming functions */
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static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
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{
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struct ext4_sb_info *sbi = EXT4_SB(sb);
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int offset = offsetof(struct mmp_struct, mmp_checksum);
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__u32 csum;
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csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
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return cpu_to_le32(csum);
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}
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static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
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{
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if (!ext4_has_metadata_csum(sb))
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return 1;
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return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
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}
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static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
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{
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if (!ext4_has_metadata_csum(sb))
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return;
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mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
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}
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/*
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* Write the MMP block using REQ_SYNC to try to get the block on-disk
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* faster.
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*/
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static int write_mmp_block_thawed(struct super_block *sb,
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struct buffer_head *bh)
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{
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struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
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ext4_mmp_csum_set(sb, mmp);
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lock_buffer(bh);
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bh->b_end_io = end_buffer_write_sync;
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get_bh(bh);
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submit_bh(REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO, bh);
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wait_on_buffer(bh);
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if (unlikely(!buffer_uptodate(bh)))
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return -EIO;
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return 0;
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}
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static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
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{
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int err;
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/*
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* We protect against freezing so that we don't create dirty buffers
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* on frozen filesystem.
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*/
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sb_start_write(sb);
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err = write_mmp_block_thawed(sb, bh);
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sb_end_write(sb);
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return err;
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}
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/*
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* Read the MMP block. It _must_ be read from disk and hence we clear the
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* uptodate flag on the buffer.
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*/
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static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
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ext4_fsblk_t mmp_block)
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{
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struct mmp_struct *mmp;
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int ret;
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if (*bh)
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clear_buffer_uptodate(*bh);
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/* This would be sb_bread(sb, mmp_block), except we need to be sure
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* that the MD RAID device cache has been bypassed, and that the read
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* is not blocked in the elevator. */
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if (!*bh) {
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*bh = sb_getblk(sb, mmp_block);
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if (!*bh) {
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ret = -ENOMEM;
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goto warn_exit;
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}
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}
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lock_buffer(*bh);
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ret = ext4_read_bh(*bh, REQ_META | REQ_PRIO, NULL);
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if (ret)
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goto warn_exit;
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mmp = (struct mmp_struct *)((*bh)->b_data);
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if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
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ret = -EFSCORRUPTED;
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goto warn_exit;
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}
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if (!ext4_mmp_csum_verify(sb, mmp)) {
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ret = -EFSBADCRC;
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goto warn_exit;
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}
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return 0;
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warn_exit:
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brelse(*bh);
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*bh = NULL;
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ext4_warning(sb, "Error %d while reading MMP block %llu",
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ret, mmp_block);
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return ret;
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}
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/*
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* Dump as much information as possible to help the admin.
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*/
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void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
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const char *function, unsigned int line, const char *msg)
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{
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__ext4_warning(sb, function, line, "%s", msg);
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__ext4_warning(sb, function, line,
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"MMP failure info: last update time: %llu, last update node: %.*s, last update device: %.*s",
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(unsigned long long)le64_to_cpu(mmp->mmp_time),
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(int)sizeof(mmp->mmp_nodename), mmp->mmp_nodename,
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(int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
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}
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/*
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* kmmpd will update the MMP sequence every s_mmp_update_interval seconds
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*/
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static int kmmpd(void *data)
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{
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struct super_block *sb = data;
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struct ext4_super_block *es = EXT4_SB(sb)->s_es;
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struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
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struct mmp_struct *mmp;
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ext4_fsblk_t mmp_block;
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u32 seq = 0;
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unsigned long failed_writes = 0;
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int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
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unsigned mmp_check_interval;
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unsigned long last_update_time;
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unsigned long diff;
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int retval = 0;
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mmp_block = le64_to_cpu(es->s_mmp_block);
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mmp = (struct mmp_struct *)(bh->b_data);
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mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
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/*
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* Start with the higher mmp_check_interval and reduce it if
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* the MMP block is being updated on time.
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*/
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mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
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EXT4_MMP_MIN_CHECK_INTERVAL);
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mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
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memcpy(mmp->mmp_nodename, init_utsname()->nodename,
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sizeof(mmp->mmp_nodename));
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while (!kthread_should_stop() && !ext4_forced_shutdown(sb)) {
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if (!ext4_has_feature_mmp(sb)) {
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ext4_warning(sb, "kmmpd being stopped since MMP feature"
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" has been disabled.");
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goto wait_to_exit;
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}
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if (++seq > EXT4_MMP_SEQ_MAX)
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seq = 1;
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mmp->mmp_seq = cpu_to_le32(seq);
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mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
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last_update_time = jiffies;
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retval = write_mmp_block(sb, bh);
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/*
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* Don't spew too many error messages. Print one every
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* (s_mmp_update_interval * 60) seconds.
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*/
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if (retval) {
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if ((failed_writes % 60) == 0) {
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ext4_error_err(sb, -retval,
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"Error writing to MMP block");
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}
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failed_writes++;
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}
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diff = jiffies - last_update_time;
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if (diff < mmp_update_interval * HZ)
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schedule_timeout_interruptible(mmp_update_interval *
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HZ - diff);
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/*
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* We need to make sure that more than mmp_check_interval
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* seconds have not passed since writing. If that has happened
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* we need to check if the MMP block is as we left it.
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*/
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diff = jiffies - last_update_time;
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if (diff > mmp_check_interval * HZ) {
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struct buffer_head *bh_check = NULL;
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struct mmp_struct *mmp_check;
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retval = read_mmp_block(sb, &bh_check, mmp_block);
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if (retval) {
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ext4_error_err(sb, -retval,
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"error reading MMP data: %d",
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retval);
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goto wait_to_exit;
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}
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mmp_check = (struct mmp_struct *)(bh_check->b_data);
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if (mmp->mmp_seq != mmp_check->mmp_seq ||
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memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
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sizeof(mmp->mmp_nodename))) {
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dump_mmp_msg(sb, mmp_check,
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"Error while updating MMP info. "
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"The filesystem seems to have been"
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" multiply mounted.");
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ext4_error_err(sb, EBUSY, "abort");
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put_bh(bh_check);
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retval = -EBUSY;
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goto wait_to_exit;
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}
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put_bh(bh_check);
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}
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/*
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* Adjust the mmp_check_interval depending on how much time
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* it took for the MMP block to be written.
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*/
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mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
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EXT4_MMP_MAX_CHECK_INTERVAL),
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EXT4_MMP_MIN_CHECK_INTERVAL);
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mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
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}
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/*
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* Unmount seems to be clean.
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*/
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mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
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mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
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retval = write_mmp_block(sb, bh);
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wait_to_exit:
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while (!kthread_should_stop()) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (!kthread_should_stop())
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schedule();
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}
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set_current_state(TASK_RUNNING);
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return retval;
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}
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void ext4_stop_mmpd(struct ext4_sb_info *sbi)
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{
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if (sbi->s_mmp_tsk) {
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kthread_stop(sbi->s_mmp_tsk);
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brelse(sbi->s_mmp_bh);
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sbi->s_mmp_tsk = NULL;
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}
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}
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/*
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* Get a random new sequence number but make sure it is not greater than
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* EXT4_MMP_SEQ_MAX.
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*/
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static unsigned int mmp_new_seq(void)
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{
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return get_random_u32_below(EXT4_MMP_SEQ_MAX + 1);
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}
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/*
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* Protect the filesystem from being mounted more than once.
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*/
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int ext4_multi_mount_protect(struct super_block *sb,
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ext4_fsblk_t mmp_block)
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{
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struct ext4_super_block *es = EXT4_SB(sb)->s_es;
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struct buffer_head *bh = NULL;
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struct mmp_struct *mmp = NULL;
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u32 seq;
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unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
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unsigned int wait_time = 0;
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int retval;
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if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
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mmp_block >= ext4_blocks_count(es)) {
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ext4_warning(sb, "Invalid MMP block in superblock");
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retval = -EINVAL;
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goto failed;
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}
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retval = read_mmp_block(sb, &bh, mmp_block);
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if (retval)
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goto failed;
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mmp = (struct mmp_struct *)(bh->b_data);
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if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
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mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
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/*
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* If check_interval in MMP block is larger, use that instead of
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* update_interval from the superblock.
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*/
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if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
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mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
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seq = le32_to_cpu(mmp->mmp_seq);
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if (seq == EXT4_MMP_SEQ_CLEAN)
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goto skip;
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if (seq == EXT4_MMP_SEQ_FSCK) {
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dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
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retval = -EBUSY;
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goto failed;
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}
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wait_time = min(mmp_check_interval * 2 + 1,
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mmp_check_interval + 60);
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/* Print MMP interval if more than 20 secs. */
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if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
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ext4_warning(sb, "MMP interval %u higher than expected, please"
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" wait.\n", wait_time * 2);
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if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
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ext4_warning(sb, "MMP startup interrupted, failing mount\n");
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retval = -ETIMEDOUT;
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goto failed;
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}
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retval = read_mmp_block(sb, &bh, mmp_block);
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if (retval)
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goto failed;
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mmp = (struct mmp_struct *)(bh->b_data);
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if (seq != le32_to_cpu(mmp->mmp_seq)) {
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dump_mmp_msg(sb, mmp,
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"Device is already active on another node.");
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retval = -EBUSY;
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goto failed;
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}
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skip:
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/*
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* write a new random sequence number.
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*/
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seq = mmp_new_seq();
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mmp->mmp_seq = cpu_to_le32(seq);
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/*
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* On mount / remount we are protected against fs freezing (by s_umount
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* semaphore) and grabbing freeze protection upsets lockdep
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*/
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retval = write_mmp_block_thawed(sb, bh);
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if (retval)
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goto failed;
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/*
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* wait for MMP interval and check mmp_seq.
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*/
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if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
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ext4_warning(sb, "MMP startup interrupted, failing mount");
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retval = -ETIMEDOUT;
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goto failed;
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}
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retval = read_mmp_block(sb, &bh, mmp_block);
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if (retval)
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goto failed;
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mmp = (struct mmp_struct *)(bh->b_data);
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if (seq != le32_to_cpu(mmp->mmp_seq)) {
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dump_mmp_msg(sb, mmp,
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"Device is already active on another node.");
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retval = -EBUSY;
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goto failed;
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}
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EXT4_SB(sb)->s_mmp_bh = bh;
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BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
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snprintf(mmp->mmp_bdevname, sizeof(mmp->mmp_bdevname),
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"%pg", bh->b_bdev);
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/*
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* Start a kernel thread to update the MMP block periodically.
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*/
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EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
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(int)sizeof(mmp->mmp_bdevname),
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mmp->mmp_bdevname);
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if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
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EXT4_SB(sb)->s_mmp_tsk = NULL;
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ext4_warning(sb, "Unable to create kmmpd thread for %s.",
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sb->s_id);
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retval = -ENOMEM;
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goto failed;
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}
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return 0;
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failed:
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brelse(bh);
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return retval;
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}
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