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    Subject[PATCH 3.16 205/410] pipe: make account_pipe_buffers() return a value, and use it
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>

    commit 9c87bcf0a31b338dc8a69a5d251a037565a94e13 upstream.

    This is an optional patch, to provide a small performance
    improvement. Alter account_pipe_buffers() so that it returns the
    new value in user->pipe_bufs. This means that we can refactor
    too_many_pipe_buffers_soft() and too_many_pipe_buffers_hard() to
    avoid the costs of repeated use of atomic_long_read() to get the
    value user->pipe_bufs.

    Link: http://lkml.kernel.org/r/93e5f193-1e5e-3e1f-3a20-eae79b7e1310@gmail.com
    Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
    Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
    Cc: Willy Tarreau <w@1wt.eu>
    Cc: <socketpair@gmail.com>
    Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Cc: Jens Axboe <axboe@fb.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/pipe.c | 36 ++++++++++++++++++------------------
    1 file changed, 18 insertions(+), 18 deletions(-)

    --- a/fs/pipe.c
    +++ b/fs/pipe.c
    @@ -590,22 +590,20 @@ pipe_fasync(int fd, struct file *filp, i
    return retval;
    }

    -static void account_pipe_buffers(struct user_struct *user,
    +static unsigned long account_pipe_buffers(struct user_struct *user,
    unsigned long old, unsigned long new)
    {
    - atomic_long_add(new - old, &user->pipe_bufs);
    + return atomic_long_add_return(new - old, &user->pipe_bufs);
    }

    -static bool too_many_pipe_buffers_soft(struct user_struct *user)
    +static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
    {
    - return pipe_user_pages_soft &&
    - atomic_long_read(&user->pipe_bufs) >= pipe_user_pages_soft;
    + return pipe_user_pages_soft && user_bufs >= pipe_user_pages_soft;
    }

    -static bool too_many_pipe_buffers_hard(struct user_struct *user)
    +static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
    {
    - return pipe_user_pages_hard &&
    - atomic_long_read(&user->pipe_bufs) >= pipe_user_pages_hard;
    + return pipe_user_pages_hard && user_bufs >= pipe_user_pages_hard;
    }

    struct pipe_inode_info *alloc_pipe_info(void)
    @@ -613,19 +611,20 @@ struct pipe_inode_info *alloc_pipe_info(
    struct pipe_inode_info *pipe;
    unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
    struct user_struct *user = get_current_user();
    + unsigned long user_bufs;

    pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
    if (pipe == NULL)
    goto out_free_uid;

    - account_pipe_buffers(user, 0, pipe_bufs);
    + user_bufs = account_pipe_buffers(user, 0, pipe_bufs);

    - if (too_many_pipe_buffers_soft(user)) {
    - account_pipe_buffers(user, pipe_bufs, 1);
    + if (too_many_pipe_buffers_soft(user_bufs)) {
    + user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
    pipe_bufs = 1;
    }

    - if (too_many_pipe_buffers_hard(user))
    + if (too_many_pipe_buffers_hard(user_bufs))
    goto out_revert_acct;

    pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
    @@ -641,7 +640,7 @@ struct pipe_inode_info *alloc_pipe_info(
    }

    out_revert_acct:
    - account_pipe_buffers(user, pipe_bufs, 0);
    + (void) account_pipe_buffers(user, pipe_bufs, 0);
    kfree(pipe);
    out_free_uid:
    free_uid(user);
    @@ -652,7 +651,7 @@ void free_pipe_info(struct pipe_inode_in
    {
    int i;

    - account_pipe_buffers(pipe->user, pipe->buffers, 0);
    + (void) account_pipe_buffers(pipe->user, pipe->buffers, 0);
    free_uid(pipe->user);
    for (i = 0; i < pipe->buffers; i++) {
    struct pipe_buffer *buf = pipe->bufs + i;
    @@ -1022,6 +1021,7 @@ static long pipe_set_size(struct pipe_in
    {
    struct pipe_buffer *bufs;
    unsigned int size, nr_pages;
    + unsigned long user_bufs;
    long ret = 0;

    size = round_pipe_size(arg);
    @@ -1041,11 +1041,11 @@ static long pipe_set_size(struct pipe_in
    size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
    return -EPERM;

    - account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
    + user_bufs = account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);

    if (nr_pages > pipe->buffers &&
    - (too_many_pipe_buffers_hard(pipe->user) ||
    - too_many_pipe_buffers_soft(pipe->user)) &&
    + (too_many_pipe_buffers_hard(user_bufs) ||
    + too_many_pipe_buffers_soft(user_bufs)) &&
    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
    ret = -EPERM;
    goto out_revert_acct;
    @@ -1096,7 +1096,7 @@ static long pipe_set_size(struct pipe_in
    return nr_pages * PAGE_SIZE;

    out_revert_acct:
    - account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
    + (void) account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
    return ret;
    }

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