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List:       linux-kernel
Subject:    Re: [PATCH] staging: lustre: replace kzalloc with copy_from_user with memdup_user
From:       "Drokin, Oleg" <oleg.drokin () intel ! com>
Date:       2015-03-31 22:45:10
Message-ID: A7B00F94-83B4-4B13-941F-90591B4BC218 () intel ! com
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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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