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    SubjectRe: [PATCH] staging: lustre: replace kzalloc with copy_from_user with memdup_user
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    On Mar 31, 2015, at 11:57 AM, gregkh@linuxfoundation.org wrote:

    > On Tue, Mar 31, 2015 at 05:15:23PM +0200, Julia Lawall wrote:
    >> On Tue, 31 Mar 2015, Dhere, Chaitanya (C.) wrote:
    >>
    >>> This patch replaces kzalloc and copy_from_user with memdup_user call
    >>> This change was detected with coccinelle tool
    >>>
    >>> Signed-off-by: Chaitanya Dhere <cvijaydh@visteon.com>
    >>> ---
    >>> drivers/staging/lustre/lustre/llite/file.c | 11 +++--------
    >>> 1 file changed, 3 insertions(+), 8 deletions(-)
    >>>
    >>> diff --git a/drivers/staging/lustre/lustre/llite/file.c b/drivers/staging/lustre/lustre/llite/file.c
    >>> index 85e74d1..85b5567 100644
    >>> --- a/drivers/staging/lustre/lustre/llite/file.c
    >>> +++ b/drivers/staging/lustre/lustre/llite/file.c
    >>> @@ -2368,14 +2368,9 @@ ll_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
    >>> struct hsm_state_set *hss;
    >>> int rc;
    >>>
    >>> - hss = kzalloc(sizeof(*hss), GFP_NOFS);
    >>> - if (!hss)
    >>> - return -ENOMEM;
    >>> -
    >>> - if (copy_from_user(hss, (char *)arg, sizeof(*hss))) {
    >>> - OBD_FREE_PTR(hss);
    >>> - return -EFAULT;
    >>> - }
    >>> + hss = memdup_user((char *)arg, sizeof(*hss));
    >>
    >> memdup_user will use the flag GFP_KERNEL, ie (__GFP_WAIT | __GFP_IO |
    >> __GFP_FS), rather than the flag GFP_NOFS, ie (__GFP_WAIT | __GFP_IO), that
    >> is specified. I don't know if this is a problem here.
    >
    > Yes, this is a filesystem, so this can't be changed, as we can't have
    > the allocation go out and ask for more filesystem accesses in the middle
    > of trying to do a filesystem access :)

    Technically in this place we are not really holding any locks or anything else of value to cause a deadlock,
    so we might be fine here.
    More importantly, I totally missed this OBD_ALLOC replacement with kzalloc when it happened.
    In theory all OBD_ALLOC() calls add up all allocated memory in a counter and then OBD_FREE() calls
    subtract freed memory (for a poor man's memory leak detection and tracing).
    Now since it's out of match, there should have been tons of very loud warnings about it, but I don't see
    any in my logs and I wonder why.

    Julia, I wonder if you happen to have a bunch of other patches to get rid of the rest of OBD_ALLOC and OBD_FREE stuff by any chance?

    Bye,
    Oleg

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