From: Mike Rapoport <rppt@kernel.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Christoph Hellwig <hch@infradead.org>,
Helge Deller <deller@gmx.de>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Luis Chamberlain <mcgrof@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Palmer Dabbelt <palmer@dabbelt.com>,
Peter Zijlstra <peterz@infradead.org>,
Russell King <linux@armlinux.org.uk>, Song Liu <song@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Uladzislau Rezki <urezki@gmail.com>,
Will Deacon <will@kernel.org>, bpf <bpf@vger.kernel.org>,
linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
linux-modules@vger.kernel.org, linux-parisc@vger.kernel.org,
linux-riscv@lists.infradead.org,
linux-trace-kernel@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [RFC PATCH 3/7] module: [
Date: Thu, 18 Apr 2024 22:44:31 +0300 [thread overview]
Message-ID: <ZiF4H5_tGx7woaXH@kernel.org> (raw)
In-Reply-To: <A714B340-9EFB-4F27-9CD6-CFBC1BC9139F@gmail.com>
On Thu, Apr 18, 2024 at 10:31:16PM +0300, Nadav Amit wrote:
>
> > On 18 Apr 2024, at 13:20, Mike Rapoport <rppt@kernel.org> wrote:
> >
> > On Tue, Apr 16, 2024 at 12:36:08PM +0300, Nadav Amit wrote:
> >>
> >>
> >>
> >> I might be missing something, but it seems a bit racy.
> >>
> >> IIUC, module_finalize() calls alternatives_smp_module_add(). At this
> >> point, since you don’t hold the text_mutex, some might do text_poke(),
> >> e.g., by enabling/disabling static-key, and the update would be
> >> overwritten. No?
> >
> > Right :(
> > Even worse, for UP case alternatives_smp_unlock() will "patch" still empty
> > area.
> >
> > So I'm thinking about calling alternatives_smp_module_add() from an
> > additional callback after the execmem_update_copy().
> >
> > Does it make sense to you?
>
> Going over the code again - I might have just been wrong: I confused the
> alternatives and the jump-label mechanisms (as they do share a lot of
> code and characteristics).
>
> The jump-labels are updated when prepare_coming_module() is called, which
> happens after post_relocation() [which means they would be updated using
> text_poke() “inefficiently” but should be safe].
>
> The “alternatives” appear only to use text_poke() (in contrast for
> text_poke_early()) from very specific few flows, e.g.,
> common_cpu_up() -> alternatives_enable_smp().
>
> Are those flows pose a problem after boot?
Yes, common_cpu_up is called on CPU hotplug, so it's possible to have a
race between alternatives_smp_module_add() and common_cpu_up() ->
alternatives_enable_smp().
And in UP case alternatives_smp_module_add() will call
alternatives_smp_unlock() that will patch module text before it is updated.
> Anyhow, sorry for the noise.
On the contrary, I would have missed it.
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2024-04-18 19:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 16:05 [RFC PATCH 0/7] x86/module: use large ROX pages for text allocations Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 1/7] asm-generic: introduce text-patching.h Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 2/7] mm: vmalloc: don't account for number of nodes for HUGE_VMAP allocations Mike Rapoport
2024-04-12 6:07 ` Christophe Leroy
2024-04-14 7:34 ` Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 3/7] module: prepare to handle ROX allocations for text Mike Rapoport
2024-04-16 9:36 ` Nadav Amit
2024-04-18 10:20 ` Mike Rapoport
2024-04-18 19:31 ` [RFC PATCH 3/7] module: [ Nadav Amit
2024-04-18 19:44 ` Mike Rapoport [this message]
2024-04-11 16:05 ` [RFC PATCH 4/7] ftrace: Add swap_func to ftrace_process_locs() Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 5/7] x86/module: perpare module loading for ROX allocations of text Mike Rapoport
2024-04-12 9:08 ` Ingo Molnar
2024-04-14 7:35 ` Mike Rapoport
2024-04-15 10:43 ` Peter Zijlstra
2024-04-15 17:04 ` Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 6/7] execmem: add support for cache of large ROX pages Mike Rapoport
2024-04-15 10:47 ` Peter Zijlstra
2024-04-15 17:00 ` Mike Rapoport
2024-04-16 7:52 ` Peter Zijlstra
2024-04-18 10:23 ` Mike Rapoport
2024-04-11 16:05 ` [RFC PATCH 7/7] x86/module: enable ROX caches for module text Mike Rapoport
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