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Message-ID: <20140729193232.GA8153@redhat.com>
Date: Tue, 29 Jul 2014 21:32:32 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
Will Drewry <wad@...omium.org>, x86@...nel.org,
linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
linux-arch@...r.kernel.org, linux-security-module@...r.kernel.org,
Alexei Starovoitov <ast@...mgrid.com>, hpa@...or.com,
Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ
On 07/28, Andy Lutomirski wrote:
>
> @@ -1449,7 +1449,12 @@ long syscall_trace_enter(struct pt_regs *regs)
> {
> long ret = 0;
>
> - user_exit();
> + /*
> + * If TIF_NOHZ is set, we are required to call user_exit() before
> + * doing anything that could touch RCU.
> + */
> + if (test_thread_flag(TIF_NOHZ))
> + user_exit();
Personally I still think this change just adds more confusion, but I leave
this to you and Frederic.
It is not that "If TIF_NOHZ is set, we are required to call user_exit()", we
need to call user_exit() just because we enter the kernel. TIF_NOHZ is just
the implementation detail which triggers this slow path.
At least it should be correct, unless I am confused even more than I think.
Oleg.
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