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    Subject[PATCH 5.15 055/917] ext4: refresh the ext4_ext_path struct after dropping i_data_sem.
    Date
    From: yangerkun <yangerkun@huawei.com>

    commit 1811bc401aa58c7bdb0df3205aa6613b49d32127 upstream.

    After we drop i_data sem, we need to reload the ext4_ext_path
    structure since the extent tree can change once i_data_sem is
    released.

    This addresses the BUG:

    [52117.465187] ------------[ cut here ]------------
    [52117.465686] kernel BUG at fs/ext4/extents.c:1756!
    ...
    [52117.478306] Call Trace:
    [52117.478565] ext4_ext_shift_extents+0x3ee/0x710
    [52117.479020] ext4_fallocate+0x139c/0x1b40
    [52117.479405] ? __do_sys_newfstat+0x6b/0x80
    [52117.479805] vfs_fallocate+0x151/0x4b0
    [52117.480177] ksys_fallocate+0x4a/0xa0
    [52117.480533] __x64_sys_fallocate+0x22/0x30
    [52117.480930] do_syscall_64+0x35/0x80
    [52117.481277] entry_SYSCALL_64_after_hwframe+0x44/0xae
    [52117.481769] RIP: 0033:0x7fa062f855ca

    Cc: stable@kernel.org
    Link: https://lore.kernel.org/r/20210903062748.4118886-4-yangerkun@huawei.com
    Signed-off-by: yangerkun <yangerkun@huawei.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/ext4/extents.c | 14 +++++++++++++-
    1 file changed, 13 insertions(+), 1 deletion(-)

    --- a/fs/ext4/extents.c
    +++ b/fs/ext4/extents.c
    @@ -5012,8 +5012,11 @@ ext4_ext_shift_path_extents(struct ext4_
    restart_credits = ext4_writepage_trans_blocks(inode);
    err = ext4_datasem_ensure_credits(handle, inode, credits,
    restart_credits, 0);
    - if (err)
    + if (err) {
    + if (err > 0)
    + err = -EAGAIN;
    goto out;
    + }

    err = ext4_ext_get_access(handle, inode, path + depth);
    if (err)
    @@ -5087,6 +5090,7 @@ ext4_ext_shift_extents(struct inode *ino
    int ret = 0, depth;
    struct ext4_extent *extent;
    ext4_lblk_t stop, *iterator, ex_start, ex_end;
    + ext4_lblk_t tmp = EXT_MAX_BLOCKS;

    /* Let path point to the last extent */
    path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL,
    @@ -5140,11 +5144,15 @@ ext4_ext_shift_extents(struct inode *ino
    * till we reach stop. In case of right shift, iterator points to stop
    * and it is decreased till we reach start.
    */
    +again:
    if (SHIFT == SHIFT_LEFT)
    iterator = &start;
    else
    iterator = &stop;

    + if (tmp != EXT_MAX_BLOCKS)
    + *iterator = tmp;
    +
    /*
    * Its safe to start updating extents. Start and stop are unsigned, so
    * in case of right shift if extent with 0 block is reached, iterator
    @@ -5173,6 +5181,7 @@ ext4_ext_shift_extents(struct inode *ino
    }
    }

    + tmp = *iterator;
    if (SHIFT == SHIFT_LEFT) {
    extent = EXT_LAST_EXTENT(path[depth].p_hdr);
    *iterator = le32_to_cpu(extent->ee_block) +
    @@ -5191,6 +5200,9 @@ ext4_ext_shift_extents(struct inode *ino
    }
    ret = ext4_ext_shift_path_extents(path, shift, inode,
    handle, SHIFT);
    + /* iterator can be NULL which means we should break */
    + if (ret == -EAGAIN)
    + goto again;
    if (ret)
    break;
    }

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