linux-kernel - Re: [PATCH V7 4/4] softirq: Allow early break the softirq processing loop

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20200924231048.GD19346@lenoir>
Date:   Fri, 25 Sep 2020 01:10:48 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     qianjun.kernel@...il.com, peterz@...radead.org, will@...nel.org,
        luto@...nel.org, linux-kernel@...r.kernel.org,
        laoar.shao@...il.com, qais.yousef@....com, urezki@...il.com
Subject: Re: [PATCH V7 4/4] softirq: Allow early break the softirq processing
 loop

On Fri, Sep 25, 2020 at 01:08:11AM +0200, Frederic Weisbecker wrote:
> On Thu, Sep 24, 2020 at 05:37:42PM +0200, Thomas Gleixner wrote:
> > Subject: softirq; Prevent starvation of higher softirq vectors
> > From: Thomas Gleixner <tglx@...utronix.de>
> > Date: Thu, 24 Sep 2020 10:40:24 +0200
> > 
> > From: Thomas Gleixner <tglx@...utronix.de>
> > 
> > The early termination of the softirq processing loop can lead to starvation
> > of the higher numbered soft interrupt vectors because each run starts at
> > the lowest bit. If the loop terminates then the already processed bits can
> > be raised again before the next loop starts. If these lower bits run into
> > the termination again, then a re-raise might starve the higher bits forever.
> > 
> > To prevent this, store the leftovers of the previous run in the upper 16
> > bit of the local softirq_pending storage and ensure that these are
> > processed before any newly raised bits are handled.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  kernel/softirq.c |   58 +++++++++++++++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 50 insertions(+), 8 deletions(-)
> > 
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -259,11 +259,23 @@ static inline bool __softirq_needs_break
> >  	return need_resched() || __softirq_timeout(tbreak);
> >  }
> >  
> > +/*
> > + * local_softirq_pending() is split into two 16 bit words. The low word
> > + * contains the bits set by raise_softirq(), the high word contains pending
> > + * bits which have not been processed in an early terminated run. This is
> > + * required to prevent starvation of the higher numbered softirqs.
> > + */
> > +#define SIRQ_PREV_SHIFT		16
> 
> Note that in the case of x86, irq_start.__softirq_pending is a u16.

irq_stat even