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    Subject[PATCH 3.5 33/64] nilfs2: fix issue with race condition of competition between segments for dirty blocks
    Date
    3.5.7.24 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Vyacheslav Dubeyko <slava@dubeyko.com>

    commit 7f42ec3941560f0902fe3671e36f2c20ffd3af0a upstream.

    Many NILFS2 users were reported about strange file system corruption
    (for example):

    NILFS: bad btree node (blocknr=185027): level = 0, flags = 0x0, nchildren = 768
    NILFS error (device sda4): nilfs_bmap_last_key: broken bmap (inode number=11540)

    But such error messages are consequence of file system's issue that takes
    place more earlier. Fortunately, Jerome Poulin <jeromepoulin@gmail.com>
    and Anton Eliasson <devel@antoneliasson.se> were reported about another
    issue not so recently. These reports describe the issue with segctor
    thread's crash:

    BUG: unable to handle kernel paging request at 0000000000004c83
    IP: nilfs_end_page_io+0x12/0xd0 [nilfs2]

    Call Trace:
    nilfs_segctor_do_construct+0xf25/0x1b20 [nilfs2]
    nilfs_segctor_construct+0x17b/0x290 [nilfs2]
    nilfs_segctor_thread+0x122/0x3b0 [nilfs2]
    kthread+0xc0/0xd0
    ret_from_fork+0x7c/0xb0

    These two issues have one reason. This reason can raise third issue
    too. Third issue results in hanging of segctor thread with eating of
    100% CPU.

    REPRODUCING PATH:

    One of the possible way or the issue reproducing was described by
    Jermoe me Poulin <jeromepoulin@gmail.com>:

    1. init S to get to single user mode.
    2. sysrq+E to make sure only my shell is running
    3. start network-manager to get my wifi connection up
    4. login as root and launch "screen"
    5. cd /boot/log/nilfs which is a ext3 mount point and can log when NILFS dies.
    6. lscp | xz -9e > lscp.txt.xz
    7. mount my snapshot using mount -o cp=3360839,ro /dev/vgUbuntu/root /mnt/nilfs
    8. start a screen to dump /proc/kmsg to text file since rsyslog is killed
    9. start a screen and launch strace -f -o find-cat.log -t find
    /mnt/nilfs -type f -exec cat {} > /dev/null \;
    10. start a screen and launch strace -f -o apt-get.log -t apt-get update
    11. launch the last command again as it did not crash the first time
    12. apt-get crashes
    13. ps aux > ps-aux-crashed.log
    13. sysrq+W
    14. sysrq+E wait for everything to terminate
    15. sysrq+SUSB

    Simplified way of the issue reproducing is starting kernel compilation
    task and "apt-get update" in parallel.

    REPRODUCIBILITY:

    The issue is reproduced not stable [60% - 80%]. It is very important to
    have proper environment for the issue reproducing. The critical
    conditions for successful reproducing:

    (1) It should have big modified file by mmap() way.

    (2) This file should have the count of dirty blocks are greater that
    several segments in size (for example, two or three) from time to time
    during processing.

    (3) It should be intensive background activity of files modification
    in another thread.

    INVESTIGATION:

    First of all, it is possible to see that the reason of crash is not valid
    page address:

    NILFS [nilfs_segctor_complete_write]:2100 bh->b_count 0, bh->b_blocknr 13895680, bh->b_size 13897727, bh->b_page 0000000000001a82
    NILFS [nilfs_segctor_complete_write]:2101 segbuf->sb_segnum 6783

    Moreover, value of b_page (0x1a82) is 6786. This value looks like segment
    number. And b_blocknr with b_size values look like block numbers. So,
    buffer_head's pointer points on not proper address value.

    Detailed investigation of the issue is discovered such picture:

    [-----------------------------SEGMENT 6783-------------------------------]
    NILFS [nilfs_segctor_do_construct]:2310 nilfs_segctor_begin_construction
    NILFS [nilfs_segctor_do_construct]:2321 nilfs_segctor_collect
    NILFS [nilfs_segctor_do_construct]:2336 nilfs_segctor_assign
    NILFS [nilfs_segctor_do_construct]:2367 nilfs_segctor_update_segusage
    NILFS [nilfs_segctor_do_construct]:2371 nilfs_segctor_prepare_write
    NILFS [nilfs_segctor_do_construct]:2376 nilfs_add_checksums_on_logs
    NILFS [nilfs_segctor_do_construct]:2381 nilfs_segctor_write
    NILFS [nilfs_segbuf_submit_bio]:464 bio->bi_sector 111149024, segbuf->sb_segnum 6783

    [-----------------------------SEGMENT 6784-------------------------------]
    NILFS [nilfs_segctor_do_construct]:2310 nilfs_segctor_begin_construction
    NILFS [nilfs_segctor_do_construct]:2321 nilfs_segctor_collect
    NILFS [nilfs_lookup_dirty_data_buffers]:782 bh->b_count 1, bh->b_page ffffea000709b000, page->index 0, i_ino 1033103, i_size 25165824
    NILFS [nilfs_lookup_dirty_data_buffers]:783 bh->b_assoc_buffers.next ffff8802174a6798, bh->b_assoc_buffers.prev ffff880221cffee8
    NILFS [nilfs_segctor_do_construct]:2336 nilfs_segctor_assign
    NILFS [nilfs_segctor_do_construct]:2367 nilfs_segctor_update_segusage
    NILFS [nilfs_segctor_do_construct]:2371 nilfs_segctor_prepare_write
    NILFS [nilfs_segctor_do_construct]:2376 nilfs_add_checksums_on_logs
    NILFS [nilfs_segctor_do_construct]:2381 nilfs_segctor_write
    NILFS [nilfs_segbuf_submit_bh]:575 bh->b_count 1, bh->b_page ffffea000709b000, page->index 0, i_ino 1033103, i_size 25165824
    NILFS [nilfs_segbuf_submit_bh]:576 segbuf->sb_segnum 6784
    NILFS [nilfs_segbuf_submit_bh]:577 bh->b_assoc_buffers.next ffff880218a0d5f8, bh->b_assoc_buffers.prev ffff880218bcdf50
    NILFS [nilfs_segbuf_submit_bio]:464 bio->bi_sector 111150080, segbuf->sb_segnum 6784, segbuf->sb_nbio 0
    [----------] ditto
    NILFS [nilfs_segbuf_submit_bio]:464 bio->bi_sector 111164416, segbuf->sb_segnum 6784, segbuf->sb_nbio 15

    [-----------------------------SEGMENT 6785-------------------------------]
    NILFS [nilfs_segctor_do_construct]:2310 nilfs_segctor_begin_construction
    NILFS [nilfs_segctor_do_construct]:2321 nilfs_segctor_collect
    NILFS [nilfs_lookup_dirty_data_buffers]:782 bh->b_count 2, bh->b_page ffffea000709b000, page->index 0, i_ino 1033103, i_size 25165824
    NILFS [nilfs_lookup_dirty_data_buffers]:783 bh->b_assoc_buffers.next ffff880219277e80, bh->b_assoc_buffers.prev ffff880221cffc88
    NILFS [nilfs_segctor_do_construct]:2367 nilfs_segctor_update_segusage
    NILFS [nilfs_segctor_do_construct]:2371 nilfs_segctor_prepare_write
    NILFS [nilfs_segctor_do_construct]:2376 nilfs_add_checksums_on_logs
    NILFS [nilfs_segctor_do_construct]:2381 nilfs_segctor_write
    NILFS [nilfs_segbuf_submit_bh]:575 bh->b_count 2, bh->b_page ffffea000709b000, page->index 0, i_ino 1033103, i_size 25165824
    NILFS [nilfs_segbuf_submit_bh]:576 segbuf->sb_segnum 6785
    NILFS [nilfs_segbuf_submit_bh]:577 bh->b_assoc_buffers.next ffff880218a0d5f8, bh->b_assoc_buffers.prev ffff880222cc7ee8
    NILFS [nilfs_segbuf_submit_bio]:464 bio->bi_sector 111165440, segbuf->sb_segnum 6785, segbuf->sb_nbio 0
    [----------] ditto
    NILFS [nilfs_segbuf_submit_bio]:464 bio->bi_sector 111177728, segbuf->sb_segnum 6785, segbuf->sb_nbio 12

    NILFS [nilfs_segctor_do_construct]:2399 nilfs_segctor_wait
    NILFS [nilfs_segbuf_wait]:676 segbuf->sb_segnum 6783
    NILFS [nilfs_segbuf_wait]:676 segbuf->sb_segnum 6784
    NILFS [nilfs_segbuf_wait]:676 segbuf->sb_segnum 6785

    NILFS [nilfs_segctor_complete_write]:2100 bh->b_count 0, bh->b_blocknr 13895680, bh->b_size 13897727, bh->b_page 0000000000001a82

    BUG: unable to handle kernel paging request at 0000000000001a82
    IP: [<ffffffffa024d0f2>] nilfs_end_page_io+0x12/0xd0 [nilfs2]

    Usually, for every segment we collect dirty files in list. Then, dirty
    blocks are gathered for every dirty file, prepared for write and
    submitted by means of nilfs_segbuf_submit_bh() call. Finally, it takes
    place complete write phase after calling nilfs_end_bio_write() on the
    block layer. Buffers/pages are marked as not dirty on final phase and
    processed files removed from the list of dirty files.

    It is possible to see that we had three prepare_write and submit_bio
    phases before segbuf_wait and complete_write phase. Moreover, segments
    compete between each other for dirty blocks because on every iteration
    of segments processing dirty buffer_heads are added in several lists of
    payload_buffers:

    [SEGMENT 6784]: bh->b_assoc_buffers.next ffff880218a0d5f8, bh->b_assoc_buffers.prev ffff880218bcdf50
    [SEGMENT 6785]: bh->b_assoc_buffers.next ffff880218a0d5f8, bh->b_assoc_buffers.prev ffff880222cc7ee8

    The next pointer is the same but prev pointer has changed. It means
    that buffer_head has next pointer from one list but prev pointer from
    another. Such modification can be made several times. And, finally, it
    can be resulted in various issues: (1) segctor hanging, (2) segctor
    crashing, (3) file system metadata corruption.

    FIX:
    This patch adds:

    (1) setting of BH_Async_Write flag in nilfs_segctor_prepare_write()
    for every proccessed dirty block;

    (2) checking of BH_Async_Write flag in
    nilfs_lookup_dirty_data_buffers() and
    nilfs_lookup_dirty_node_buffers();

    (3) clearing of BH_Async_Write flag in nilfs_segctor_complete_write(),
    nilfs_abort_logs(), nilfs_forget_buffer(), nilfs_clear_dirty_page().

    Reported-by: Jerome Poulin <jeromepoulin@gmail.com>
    Reported-by: Anton Eliasson <devel@antoneliasson.se>
    Cc: Paul Fertser <fercerpav@gmail.com>
    Cc: ARAI Shun-ichi <hermes@ceres.dti.ne.jp>
    Cc: Piotr Szymaniak <szarpaj@grubelek.pl>
    Cc: Juan Barry Manuel Canham <Linux@riotingpacifist.net>
    Cc: Zahid Chowdhury <zahid.chowdhury@starsolutions.com>
    Cc: Elmer Zhang <freeboy6716@gmail.com>
    Cc: Kenneth Langga <klangga@gmail.com>
    Signed-off-by: Vyacheslav Dubeyko <slava@dubeyko.com>
    Acked-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    [ luis: backported to 3.5:
    - nilfs_clear_dirty_page() has not been separated from
    nilfs_clear_dirty_pages() ]
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    fs/nilfs2/page.c | 2 ++
    fs/nilfs2/segment.c | 11 +++++++++--
    2 files changed, 11 insertions(+), 2 deletions(-)

    diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
    index 3e7b2a0..f45b83f 100644
    --- a/fs/nilfs2/page.c
    +++ b/fs/nilfs2/page.c
    @@ -94,6 +94,7 @@ void nilfs_forget_buffer(struct buffer_head *bh)
    clear_buffer_nilfs_volatile(bh);
    clear_buffer_nilfs_checked(bh);
    clear_buffer_nilfs_redirected(bh);
    + clear_buffer_async_write(bh);
    clear_buffer_dirty(bh);
    if (nilfs_page_buffers_clean(page))
    __nilfs_clear_page_dirty(page);
    @@ -390,6 +391,7 @@ void nilfs_clear_dirty_pages(struct address_space *mapping)
    bh = head = page_buffers(page);
    do {
    lock_buffer(bh);
    + clear_buffer_async_write(bh);
    clear_buffer_dirty(bh);
    clear_buffer_nilfs_volatile(bh);
    clear_buffer_nilfs_checked(bh);
    diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
    index 88e11fb..8992b33 100644
    --- a/fs/nilfs2/segment.c
    +++ b/fs/nilfs2/segment.c
    @@ -662,7 +662,7 @@ static size_t nilfs_lookup_dirty_data_buffers(struct inode *inode,

    bh = head = page_buffers(page);
    do {
    - if (!buffer_dirty(bh))
    + if (!buffer_dirty(bh) || buffer_async_write(bh))
    continue;
    get_bh(bh);
    list_add_tail(&bh->b_assoc_buffers, listp);
    @@ -696,7 +696,8 @@ static void nilfs_lookup_dirty_node_buffers(struct inode *inode,
    for (i = 0; i < pagevec_count(&pvec); i++) {
    bh = head = page_buffers(pvec.pages[i]);
    do {
    - if (buffer_dirty(bh)) {
    + if (buffer_dirty(bh) &&
    + !buffer_async_write(bh)) {
    get_bh(bh);
    list_add_tail(&bh->b_assoc_buffers,
    listp);
    @@ -1576,6 +1577,7 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)

    list_for_each_entry(bh, &segbuf->sb_segsum_buffers,
    b_assoc_buffers) {
    + set_buffer_async_write(bh);
    if (bh->b_page != bd_page) {
    if (bd_page) {
    lock_page(bd_page);
    @@ -1589,6 +1591,7 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)

    list_for_each_entry(bh, &segbuf->sb_payload_buffers,
    b_assoc_buffers) {
    + set_buffer_async_write(bh);
    if (bh == segbuf->sb_super_root) {
    if (bh->b_page != bd_page) {
    lock_page(bd_page);
    @@ -1674,6 +1677,7 @@ static void nilfs_abort_logs(struct list_head *logs, int err)
    list_for_each_entry(segbuf, logs, sb_list) {
    list_for_each_entry(bh, &segbuf->sb_segsum_buffers,
    b_assoc_buffers) {
    + clear_buffer_async_write(bh);
    if (bh->b_page != bd_page) {
    if (bd_page)
    end_page_writeback(bd_page);
    @@ -1683,6 +1687,7 @@ static void nilfs_abort_logs(struct list_head *logs, int err)

    list_for_each_entry(bh, &segbuf->sb_payload_buffers,
    b_assoc_buffers) {
    + clear_buffer_async_write(bh);
    if (bh == segbuf->sb_super_root) {
    if (bh->b_page != bd_page) {
    end_page_writeback(bd_page);
    @@ -1752,6 +1757,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
    b_assoc_buffers) {
    set_buffer_uptodate(bh);
    clear_buffer_dirty(bh);
    + clear_buffer_async_write(bh);
    if (bh->b_page != bd_page) {
    if (bd_page)
    end_page_writeback(bd_page);
    @@ -1773,6 +1779,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
    b_assoc_buffers) {
    set_buffer_uptodate(bh);
    clear_buffer_dirty(bh);
    + clear_buffer_async_write(bh);
    clear_buffer_delay(bh);
    clear_buffer_nilfs_volatile(bh);
    clear_buffer_nilfs_redirected(bh);
    --
    1.8.3.2


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