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Date:   Thu, 30 Mar 2023 01:54:43 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Gregory Price <gregory.price@memverge.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Gregory Price <gourry.memverge@gmail.com>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
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        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>, krisman@collabora.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Jonathan Corbet <corbet@lwn.net>, shuah <shuah@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, tongtiangen@huawei.com,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of
 access_ok
Message-ID: <20230329235442.GA10790@redhat.com>
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On 03/29, Gregory Price wrote:
>
> Last note on this before I push up another patch set.
>
> The change from __get_user to get_user also introduces a call to
> might_fault() which adds a larger callstack for every syscall /
> dispatch.  This turns into a might_sleep and might_reschedule, which
> represent a very different pattern of execution from before.

might_fault() is nop unless CONFIG_PROVE_LOCKING || DEBUG_ATOMIC_SLEEP.

Again, I won't really argue with task_access_ok(). Just I am not sure
2/4 gives enough justification for this new helper with unclear semantics
(until we ensure that access_ok() doesn't depend on current).

Oleg.