All of lore.kernel.org
 help / color / mirror / Atom feed
From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com, linux-riscv@lists.infradead.org,
	linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Guo Ren <guoren@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Palmer Dabbelt <palmer@dabbelt.com>
Subject: [PATCH] asm-generic/mmiowb: Allow mmiowb_set_pending() when preemptible()
Date: Thu, 16 Jul 2020 12:28:16 +0100	[thread overview]
Message-ID: <20200716112816.7356-1-will@kernel.org> (raw)

Although mmiowb() is concerned only with serialising MMIO writes occuring
in contexts where a spinlock is held, the call to mmiowb_set_pending()
from the MMIO write accessors can occur in preemptible contexts, such
as during driver probe() functions where ordering between CPUs is not
usually a concern, assuming that the task migration path provides the
necessary ordering guarantees.

Unfortunately, the default implementation of mmiowb_set_pending() is not
preempt-safe, as it makes use of a a per-cpu variable to track its
internal state. This has been reported to generate the following splat
on riscv:

 | BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
 | caller is regmap_mmio_write32le+0x1c/0x46
 | CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3-hfu+ #1
 | Call Trace:
 |  walk_stackframe+0x0/0x7a
 |  dump_stack+0x6e/0x88
 |  regmap_mmio_write32le+0x18/0x46
 |  check_preemption_disabled+0xa4/0xaa
 |  regmap_mmio_write32le+0x18/0x46
 |  regmap_mmio_write+0x26/0x44
 |  regmap_write+0x28/0x48
 |  sifive_gpio_probe+0xc0/0x1da

Although it's possible to fix the driver in this case, other splats have
been seen from other drivers, including the infamous 8250 UART, and so
it's better to address this problem in the mmiowb core itself.

Fix mmiowb_set_pending() by using the raw_cpu_ptr() to get at the mmiowb
state and then only updating the 'mmiowb_pending' field if we are not
preemptible (i.e. we have a non-zero nesting count).

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Will Deacon <will@kernel.org>
---

I can queue this in the arm64 tree as a fix, as I already have some other
fixes targetting -rc6.

 include/asm-generic/mmiowb.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/mmiowb.h b/include/asm-generic/mmiowb.h
index 9439ff037b2d..5698fca3bf56 100644
--- a/include/asm-generic/mmiowb.h
+++ b/include/asm-generic/mmiowb.h
@@ -27,7 +27,7 @@
 #include <asm/smp.h>
 
 DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
-#define __mmiowb_state()	this_cpu_ptr(&__mmiowb_state)
+#define __mmiowb_state()	raw_cpu_ptr(&__mmiowb_state)
 #else
 #define __mmiowb_state()	arch_mmiowb_state()
 #endif	/* arch_mmiowb_state */
@@ -35,7 +35,9 @@ DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
 static inline void mmiowb_set_pending(void)
 {
 	struct mmiowb_state *ms = __mmiowb_state();
-	ms->mmiowb_pending = ms->nesting_count;
+
+	if (likely(ms->nesting_count))
+		ms->mmiowb_pending = ms->nesting_count;
 }
 
 static inline void mmiowb_spin_lock(void)
-- 
2.27.0.389.gc38d7665816-goog


WARNING: multiple messages have this Message-ID
From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	kernel-team@android.com, Guo Ren <guoren@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org, Will Deacon <will@kernel.org>
Subject: [PATCH] asm-generic/mmiowb: Allow mmiowb_set_pending() when preemptible()
Date: Thu, 16 Jul 2020 12:28:16 +0100	[thread overview]
Message-ID: <20200716112816.7356-1-will@kernel.org> (raw)

Although mmiowb() is concerned only with serialising MMIO writes occuring
in contexts where a spinlock is held, the call to mmiowb_set_pending()
from the MMIO write accessors can occur in preemptible contexts, such
as during driver probe() functions where ordering between CPUs is not
usually a concern, assuming that the task migration path provides the
necessary ordering guarantees.

Unfortunately, the default implementation of mmiowb_set_pending() is not
preempt-safe, as it makes use of a a per-cpu variable to track its
internal state. This has been reported to generate the following splat
on riscv:

 | BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
 | caller is regmap_mmio_write32le+0x1c/0x46
 | CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3-hfu+ #1
 | Call Trace:
 |  walk_stackframe+0x0/0x7a
 |  dump_stack+0x6e/0x88
 |  regmap_mmio_write32le+0x18/0x46
 |  check_preemption_disabled+0xa4/0xaa
 |  regmap_mmio_write32le+0x18/0x46
 |  regmap_mmio_write+0x26/0x44
 |  regmap_write+0x28/0x48
 |  sifive_gpio_probe+0xc0/0x1da

Although it's possible to fix the driver in this case, other splats have
been seen from other drivers, including the infamous 8250 UART, and so
it's better to address this problem in the mmiowb core itself.

Fix mmiowb_set_pending() by using the raw_cpu_ptr() to get at the mmiowb
state and then only updating the 'mmiowb_pending' field if we are not
preemptible (i.e. we have a non-zero nesting count).

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Will Deacon <will@kernel.org>
---

I can queue this in the arm64 tree as a fix, as I already have some other
fixes targetting -rc6.

 include/asm-generic/mmiowb.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/mmiowb.h b/include/asm-generic/mmiowb.h
index 9439ff037b2d..5698fca3bf56 100644
--- a/include/asm-generic/mmiowb.h
+++ b/include/asm-generic/mmiowb.h
@@ -27,7 +27,7 @@
 #include <asm/smp.h>
 
 DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
-#define __mmiowb_state()	this_cpu_ptr(&__mmiowb_state)
+#define __mmiowb_state()	raw_cpu_ptr(&__mmiowb_state)
 #else
 #define __mmiowb_state()	arch_mmiowb_state()
 #endif	/* arch_mmiowb_state */
@@ -35,7 +35,9 @@ DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
 static inline void mmiowb_set_pending(void)
 {
 	struct mmiowb_state *ms = __mmiowb_state();
-	ms->mmiowb_pending = ms->nesting_count;
+
+	if (likely(ms->nesting_count))
+		ms->mmiowb_pending = ms->nesting_count;
 }
 
 static inline void mmiowb_spin_lock(void)
-- 
2.27.0.389.gc38d7665816-goog


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

             reply	other threads:[~2020-07-16 11:28 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-16 11:28 Will Deacon [this message]
2020-07-16 11:28 ` Will Deacon
2020-07-16 11:54 ` Emil Renner Berthing
2020-07-16 11:54   ` Emil Renner Berthing
2020-07-16 19:00 ` Palmer Dabbelt
2020-07-16 19:00   ` Palmer Dabbelt
2020-07-16 19:00   ` Palmer Dabbelt
2020-07-17 10:43 ` Will Deacon
2020-07-17 10:43   ` Will Deacon

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200716112816.7356-1-will@kernel.org \
    --to=will@kernel.org \
    --cc=arnd@arndb.de \
    --cc=guoren@kernel.org \
    --cc=kernel-team@android.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=mpe@ellerman.id.au \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --subject='Re: [PATCH] asm-generic/mmiowb: Allow mmiowb_set_pending() when preemptible()' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.