linux-kernel - Re: [BUG] rcu: stall detected in sys_mmap with PREEMPT(full) involving timer softirq and DRM vblank disable

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Message-ID: <aV5ygyPM7J7VdmgL@casper.infradead.org>
Date: Wed, 7 Jan 2026 14:49:39 +0000
From: Matthew Wilcox <willy@...radead.org>
To: 王志 <23009200614@....xidian.edu.cn>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org, linux-mm@...ck.org,
	dri-devel@...ts.freedesktop.org, x86@...nel.org, paulmck@...nel.org,
	tglx@...utronix.de, peterz@...radead.org, akpm@...ux-foundation.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [BUG] rcu: stall detected in sys_mmap with PREEMPT(full)
 involving timer softirq and DRM vblank disable

On Wed, Jan 07, 2026 at 01:52:11PM +0800, 王志 wrote:
> Hello,
> 
> I am reporting an RCU stall detected during syzkaller-style fuzz testing.
> The stall is reported while executing sys_mmap(), with the
> rcu_preempt grace-period kthread starved for over 10 seconds. The
> observed stacks involve memory fault handling, timer softirq processing,
> and DRM vblank disable paths. With PREEMPT(full) enabled, the RCU grace
> period fails to complete.

Get your changes into syzkaller upstream, don't spam us with "i'm doing
syzbot's job".