mmp.c

Go to the documentation of this file.

#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 __u32 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);
}

int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
{
    if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
        return 1;

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

void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
{
    if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
        return;

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

/*
 * Write the MMP block using WRITE_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(WRITE_SYNC, 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;

    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) {
        get_bh(*bh);
        lock_buffer(*bh);
        (*bh)->b_end_io = end_buffer_read_sync;
        submit_bh(READ_SYNC, *bh);
        wait_on_buffer(*bh);
        if (!buffer_uptodate(*bh)) {
            brelse(*bh);
            *bh = NULL;
        }
    }
    if (!*bh) {
        ext4_warning(sb, "Error while reading MMP block %llu",
                 mmp_block);
        return -EIO;
    }

    mmp = (struct mmp_struct *)((*bh)->b_data);
    if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC ||
        !ext4_mmp_csum_verify(sb, mmp))
        return -EINVAL;

    return 0;
}

/*
 * 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, msg);
    __ext4_warning(sb, function, line,
               "MMP failure info: last update time: %llu, last update "
               "node: %s, last update device: %s\n",
               (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.");
            EXT4_SB(sb)->s_mmp_tsk = NULL;
            goto failed;
        }

        if (sb->s_flags & MS_RDONLY) {
            ext4_warning(sb, "kmmpd being stopped since filesystem "
                     "has been remounted as readonly.");
            EXT4_SB(sb)->s_mmp_tsk = NULL;
            goto failed;
        }

        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);

                EXT4_SB(sb)->s_mmp_tsk = NULL;
                goto failed;
            }

            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");
                goto failed;
            }
            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);

failed:
    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 {
        get_random_bytes(&new_seq, sizeof(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\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;
    }

    mmpd_data = kmalloc(sizeof(struct 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;
}