linux-kernel - Re: [PATCH 1/2] rwsem: add rwsem_is

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: <20130919232732.GC1615@localhost.localdomain>
Date:	Thu, 19 Sep 2013 19:27:32 -0400
From:	Josef Bacik <jbacik@...ionio.com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Josef Bacik <jbacik@...ionio.com>, <linux-btrfs@...r.kernel.org>,
	<walken@...gle.com>, <linux-kernel@...r.kernel.org>,
	<mingo@...e.hu>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] rwsem: add rwsem_is_contended V2

On Thu, Sep 19, 2013 at 06:57:27PM -0400, Peter Hurley wrote:
> On 09/19/2013 11:48 AM, Josef Bacik wrote:
> >Btrfs needs a simple way to know if it needs to let go of it's read lock on a
> >rwsem.  Introduce rwsem_is_contended to check to see if there are any waiters on
> >this rwsem currently.  This is just a hueristic, it is meant to be light and not
> >100% accurate and called by somebody already holding on to the rwsem in either
> >read or write.  Thanks,
> >
> >Signed-off-by: Josef Bacik <jbacik@...ionio.com>
> >---
> >V1->V2: took everybodys suggestions and simplified it to just one function in
> >rwsem.h so it works for both the spinlock case and non-spinlock case.
> >
> >  include/linux/rwsem.h | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> >diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> >index 0616ffe..c340493 100644
> >--- a/include/linux/rwsem.h
> >+++ b/include/linux/rwsem.h
> >@@ -75,6 +75,19 @@ do {								\
> >  } while (0)
> >
> >  /*
> >+ * This is the same regardless of which rwsem implementation that is being used.
> >+ * It is just a heuristic meant to be called by somebody alreadying holding the
> >+ * rwsem to see if somebody from  the opposite type is wanting access to the
>                                         ^^^^^^^^^^^^^
> 
> Readers can infer that at least one writer is waiting if the wait_list is
> !empty; however, writers cannot infer anything other than some other
> thread is waiting -- it could be a reader or a writer or multiples of either.
> 

Right duh, I'll fix that up.

> 
> >+ * lock.
> >+ */
> >+static inline int rwsem_is_contended(struct rw_semaphore *sem)
> >+{
> >+	if (!list_empty(&sem->wait_list))
> >+		return 1;
> >+	return 0;
> 
> How about
> 
>         return !list_empty(&sem->wait_list);
> 
> ?
> 

Another duh, thanks I'll wait for any other input and then fix this up and
resend.  Thanks,

Josef
--
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/