From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
Will Drewry <wad@chromium.org>,
x86@kernel.org, linux-arm-kernel@lists.infradead.org,
linux-mips@linux-mips.org, linux-arch@vger.kernel.org,
linux-security-module@vger.kernel.org,
Alexei Starovoitov <ast@plumgrid.com>,
hpa@zytor.com, Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ
Date: Tue, 29 Jul 2014 21:32:32 +0200 [thread overview]
Message-ID: <20140729193232.GA8153@redhat.com> (raw)
In-Reply-To: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net>
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.
WARNING: multiple messages have this Message-ID (diff)
From: oleg@redhat.com (Oleg Nesterov)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ
Date: Tue, 29 Jul 2014 21:32:32 +0200 [thread overview]
Message-ID: <20140729193232.GA8153@redhat.com> (raw)
In-Reply-To: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net>
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.
next prev parent reply other threads:[~2014-07-29 19:32 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-29 3:38 [PATCH v4 0/5] x86: two-phase syscall tracing and seccomp fastpath Andy Lutomirski
2014-07-29 3:38 ` Andy Lutomirski
2014-07-29 3:38 ` [PATCH v4 1/5] x86,x32,audit: Fix x32's AUDIT_ARCH wrt audit Andy Lutomirski
2014-07-29 3:38 ` Andy Lutomirski
2014-07-29 3:38 ` [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ Andy Lutomirski
2014-07-29 3:38 ` Andy Lutomirski
2014-07-29 19:32 ` Oleg Nesterov [this message]
2014-07-29 19:32 ` Oleg Nesterov
2014-07-30 16:43 ` Frederic Weisbecker
2014-07-30 16:43 ` Frederic Weisbecker
2014-07-30 17:23 ` Andy Lutomirski
2014-07-30 17:23 ` Andy Lutomirski
2014-07-31 15:16 ` Frederic Weisbecker
2014-07-31 15:16 ` Frederic Weisbecker
2014-07-31 16:42 ` Oleg Nesterov
2014-07-31 16:42 ` Oleg Nesterov
2014-07-31 16:49 ` Frederic Weisbecker
2014-07-31 16:49 ` Frederic Weisbecker
2014-07-31 16:54 ` Oleg Nesterov
2014-07-31 16:54 ` Oleg Nesterov
2014-07-31 16:58 ` Oleg Nesterov
2014-07-31 16:58 ` Oleg Nesterov
2014-07-31 17:17 ` Frederic Weisbecker
2014-07-31 17:17 ` Frederic Weisbecker
2014-07-29 3:38 ` [PATCH v4 3/5] x86: Split syscall_trace_enter into two phases Andy Lutomirski
2014-07-29 3:38 ` Andy Lutomirski
2014-07-29 19:25 ` Oleg Nesterov
2014-07-29 19:25 ` Oleg Nesterov
2014-07-29 3:38 ` [PATCH v4 4/5] x86_64,entry: Treat regs->ax the same in fastpath and slowpath syscalls Andy Lutomirski
2014-07-29 3:38 ` [PATCH v4 4/5] x86_64, entry: " Andy Lutomirski
2014-07-29 3:38 ` [PATCH v4 5/5] x86_64,entry: Use split-phase syscall_trace_enter for 64-bit syscalls Andy Lutomirski
2014-07-29 3:38 ` [PATCH v4 5/5] x86_64, entry: " Andy Lutomirski
2014-07-29 19:20 ` [PATCH v4 0/5] x86: two-phase syscall tracing and seccomp fastpath Oleg Nesterov
2014-07-29 19:20 ` Oleg Nesterov
2014-07-29 20:54 ` Andy Lutomirski
2014-07-29 20:54 ` Andy Lutomirski
2014-07-29 23:30 ` Andy Lutomirski
2014-07-29 23:30 ` Andy Lutomirski
2014-07-30 15:32 ` Oleg Nesterov
2014-07-30 15:32 ` Oleg Nesterov
2014-07-30 16:59 ` Frederic Weisbecker
2014-07-30 16:59 ` Frederic Weisbecker
2014-07-30 17:25 ` Andy Lutomirski
2014-07-30 17:25 ` Andy Lutomirski
2014-07-31 16:56 ` H. Peter Anvin
2014-07-31 16:56 ` H. Peter Anvin
2014-07-31 17:20 ` Frederic Weisbecker
2014-07-31 17:20 ` Frederic Weisbecker
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