linux-kernel - Has slab ctor operation changed? -- was [PATCH 1/1] afs: afs_alloc_inode: use kmem_cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <32740.1392934995@warthog.procyon.org.uk>
Date:	Thu, 20 Feb 2014 22:23:15 +0000
From:	David Howells <dhowells@...hat.com>
To:	Fabian Frederick <fabf@...net.be>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	akpm <akpm@...ux-foundation.org>, cl@...ux-foundation.org
Subject: Has slab ctor operation changed? -- was [PATCH 1/1] afs: afs_alloc_inode: use kmem_cache_zalloc

Fabian Frederick <fabf@...net.be> wrote:

> afs_vnode is currently cleared with 2 memsets after allocation and 
> 1 in constructor (afs_i_init_once).
> 	-This patch calls zalloc for explicit zero fill.

Ummm...  This patch isn't necessarily correct in the substantiative portions.

Since afs_i_init_once() is called by the slab allocator during the course of
kmem_cache_alloc(), how does kmem_cache_zalloc() interact with that?

IIRC, it used to be that the ctor() function was called when the pages were
allocated to the slab - and it wasn't called again, even if the object was
allocated, deallocated and reallocated.  This means that things like locks and
lists don't need reinitialising after allocation.

So afs_i_init_once() theoretically constructs the stuff that can be reused,
and afs_alloc_inode() therefore has to clear the non-reusable state.

Of course, it's possible that the slab allocator no longer works like this...

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/