Re: [KJ] kmalloc to kzalloc patches for drivers/block [sane version]

[Paulo Marques <pmarques@grupopie.com>]

Jiri Slaby wrote:
> Om Narasimhan wrote:
> > Thanks for the comments.
> > > >
> > > > Signed off by Om Narasimhan <om.turyx@gmail.com>
> > >
> > > This is not the canonical format, per SubmittingPatches. It should be:
> > >
> > > Signed-off-by: Random J Developer <random@developer.example.org>
> > OK. I would take care of it.
> > > >  drivers/block/cciss.c    |    4 +--
> > > >  drivers/block/cpqarray.c |   72 
> > > +++++++++++++++-------------------------------
> > > >  drivers/block/loop.c     |    4 +--
> > > >  3 files changed, 25 insertions(+), 55 deletions(-)
> > >
> > > Your diffstat should have indicated to you that this should be split up
> > > better. Please (re-)read SubmittingPatches. *One* logical change per
> > > patch, most importantly.
> > OK. I would resubmit.
> > > >
> > > > diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
> > > > index 2cd3391..a800a69 100644
> > > > --- a/drivers/block/cciss.c
> > > > +++ b/drivers/block/cciss.c
> > > > @@ -900,7 +900,7 @@ #if 0                             /* 'buf_size' 
> > > member is 16-bits
> > > >                               return -EINVAL;
> > > >  #endif
> > > >                       if (iocommand.buf_size > 0) {
> > > > -                             buff = kmalloc(iocommand.buf_size, 
> > > GFP_KERNEL);
> > > > +                             buff = kzalloc(iocommand.buf_size, 
> > > GFP_KERNEL);
> > > >                               if (buff == NULL)
> > > >                                       return -EFAULT;
> > > >                       }
> > > > @@ -911,8 +911,6 @@ #endif
> > > >                                       kfree(buff);
> > > >                                       return -EFAULT;
> > > >                               }
> > > > -                     } else {
> > > > -                             memset(buff, 0, iocommand.buf_size);
> > > >                       }
> > > >                       if ((c = cmd_alloc(host, 0)) == NULL) {
> > > >                               kfree(buff);
> > >
> > > This changes performance potentially, no? The memset before was
> > > conditional upon (iocommand.Request.Type.Direction == XFER_WRITE) and
> > > now the memory will always be zero'd.
> > Yes, but not the functionality.
> > if (iocommand.buf_size > 0), code allocates using kmalloc. if
> > direction is XFER_WRITE, it does a copy_from_user(), and free()s the
> > allocated buffer, not really caring what data came in from userspace.

You really misread that code. It frees the buffer and returns -EFAULT if 
the copy_from_user _failed_. This is standard procedure and that code 
doesn't need to be changed to kzalloc.

Please only do kmalloc to k[zc]alloc changes that are really trivial. 
There is no point in risking inserting new bugs (or performance 
regressions) for some micro-space-optimization such as this.

--
Paulo Marques - www.grupopie.com

"The face of a child can say it all, especially the
mouth part of the face."
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