Re: [PATCH] staging: rtl8712: remove unnecessary alignment of pxmitpriv->pxmitbuf

[Dan Carpenter]

On Sat, May 25, 2024 at 09:32:29AM +0200, Nam Cao wrote:
> This driver wants pxmitpriv->pxmitbuf to be 4-byte aligned. This is ensured
> by allocating 4 more bytes than required with kmalloc(), then do the
> p = p + 4 - (p & 3) trick to make sure the pointer is 4-byte aligned.
> 
> This is unnecessary. Pointers from kmalloc() are already at least
> 8-byte-aligned.
> 
> Remove this alignment trick to simplify the code, and also to stop wasting
> 4 extra bytes of dynamic memory allocator.
> 
> This also gets rid of a (false) warning from kmemleak. This 4-byte-aligned
> buffer is used to store pointers from kmalloc(). For 64-bit platforms,
> pointer size is 8 bytes and kmemleak only scans for pointers in 8-byte
> blocks, thus it misses the pointers stored in this 4-byte-aligned buffer
> and thinks that these pointers have been leaked. This is just a false
> warning, not a real problem. But still, it would be nice to get rid of
> these warnings.

Are you sure it's a false positive?  I've always wondered what happens
when you do:

	p = kmalloc();
	kfree((char *)p + 4);

regards,
dan carpenter