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    Subject[PATCH AUTOSEL for 4.4 020/167] CIFS: silence lockdep splat in cifs_relock_file()
    Date
    From: Rabin Vincent <rabinv@axis.com>

    [ Upstream commit 560d388950ceda5e7c7cdef7f3d9a8ff297bbf9d ]

    cifs_relock_file() can perform a down_write() on the inode's lock_sem even
    though it was already performed in cifs_strict_readv(). Lockdep complains
    about this. AFAICS, there is no problem here, and lockdep just needs to be
    told that this nesting is OK.

    =============================================
    [ INFO: possible recursive locking detected ]
    4.11.0+ #20 Not tainted
    ---------------------------------------------
    cat/701 is trying to acquire lock:
    (&cifsi->lock_sem){++++.+}, at: cifs_reopen_file+0x7a7/0xc00

    but task is already holding lock:
    (&cifsi->lock_sem){++++.+}, at: cifs_strict_readv+0x177/0x310

    other info that might help us debug this:
    Possible unsafe locking scenario:

    CPU0
    ----
    lock(&cifsi->lock_sem);
    lock(&cifsi->lock_sem);

    *** DEADLOCK ***

    May be due to missing lock nesting notation

    1 lock held by cat/701:
    #0: (&cifsi->lock_sem){++++.+}, at: cifs_strict_readv+0x177/0x310

    stack backtrace:
    CPU: 0 PID: 701 Comm: cat Not tainted 4.11.0+ #20
    Call Trace:
    dump_stack+0x85/0xc2
    __lock_acquire+0x17dd/0x2260
    ? trace_hardirqs_on_thunk+0x1a/0x1c
    ? preempt_schedule_irq+0x6b/0x80
    lock_acquire+0xcc/0x260
    ? lock_acquire+0xcc/0x260
    ? cifs_reopen_file+0x7a7/0xc00
    down_read+0x2d/0x70
    ? cifs_reopen_file+0x7a7/0xc00
    cifs_reopen_file+0x7a7/0xc00
    ? printk+0x43/0x4b
    cifs_readpage_worker+0x327/0x8a0
    cifs_readpage+0x8c/0x2a0
    generic_file_read_iter+0x692/0xd00
    cifs_strict_readv+0x29f/0x310
    generic_file_splice_read+0x11c/0x1c0
    do_splice_to+0xa5/0xc0
    splice_direct_to_actor+0xfa/0x350
    ? generic_pipe_buf_nosteal+0x10/0x10
    do_splice_direct+0xb5/0xe0
    do_sendfile+0x278/0x3a0
    SyS_sendfile64+0xc4/0xe0
    entry_SYSCALL_64_fastpath+0x1f/0xbe

    Signed-off-by: Rabin Vincent <rabinv@axis.com>
    Acked-by: Pavel Shilovsky <pshilov@microsoft.com>
    Signed-off-by: Steve French <smfrench@gmail.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    fs/cifs/file.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/fs/cifs/file.c b/fs/cifs/file.c
    index 744be3c146f5..0141aba9eca6 100644
    --- a/fs/cifs/file.c
    +++ b/fs/cifs/file.c
    @@ -589,7 +589,7 @@ cifs_relock_file(struct cifsFileInfo *cfile)
    struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
    int rc = 0;

    - down_read(&cinode->lock_sem);
    + down_read_nested(&cinode->lock_sem, SINGLE_DEPTH_NESTING);
    if (cinode->can_cache_brlcks) {
    /* can cache locks - no need to relock */
    up_read(&cinode->lock_sem);
    --
    2.14.1
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