* [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
@ 2023-02-15 16:43 Conor Dooley
2023-02-16 11:31 ` Changbin Du
0 siblings, 1 reply; 7+ messages in thread
From: Conor Dooley @ 2023-02-15 16:43 UTC (permalink / raw
To: palmer
Cc: conor, Palmer Dabbelt, linux-riscv, Steven Rostedt, Changbin Du,
Palmer Dabbelt, Conor Dooley
From: Palmer Dabbelt <palmerdabbelt@google.com>
We're currently using stop_machine() to update ftrace, which means that
the thread that takes text_mutex during ftrace_prepare() may not be the
same as the thread that eventually patches the code. This isn't
actually a race because the lock is still held (preventing any other
concurrent accesses) and there is only one thread running during
stop_machine(), but it does trigger a lockdep failure.
This patch just elides the lockdep check during stop_machine.
Fixes: c15ac4fd60d5 ("riscv/ftrace: Add dynamic function tracer support")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
Resending this version as I am quite averse to deleting the assertion!
Changes since v2 [<20220322022331.32136-1-palmer@rivosinc.com>]:
* rebase on riscv/for-next as it as been a year.
* incorporate Changbin's suggestion that init_nop should take the lock
rather than call prepare() & post_process().
Changes since v1 [<20210506071041.417854-1-palmer@dabbelt.com>]:
* Use ftrace_arch_ocde_modify_{prepare,post_process}() to set the flag.
I remember having a reason I wanted the function when I wrote the v1,
but it's been almost a year and I forget what that was -- maybe I was
just crazy, the patch was sent at midnight.
* Fix DYNAMIC_FTRACE=n builds.
---
arch/riscv/include/asm/ftrace.h | 7 +++++++
arch/riscv/kernel/ftrace.c | 15 +++++++++++++--
arch/riscv/kernel/patch.c | 10 +++++++++-
3 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 04dad3380041..3ac7609f4ee9 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -81,8 +81,15 @@ do { \
struct dyn_ftrace;
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
#define ftrace_init_nop ftrace_init_nop
+extern int riscv_ftrace_in_stop_machine;
#endif
+#else /* CONFIG_DYNAMIC_FTRACE */
+
+#ifndef __ASSEMBLY__
+#define riscv_ftrace_in_stop_machine 0
#endif
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
#endif /* _ASM_RISCV_FTRACE_H */
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 2086f6585773..661bfa72f359 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -11,14 +11,25 @@
#include <asm/cacheflush.h>
#include <asm/patch.h>
+int riscv_ftrace_in_stop_machine;
+
#ifdef CONFIG_DYNAMIC_FTRACE
void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
{
mutex_lock(&text_mutex);
+
+ /*
+ * The code sequences we use for ftrace can't be patched while the
+ * kernel is running, so we need to use stop_machine() to modify them
+ * for now. This doesn't play nice with text_mutex, we use this flag
+ * to elide the check.
+ */
+ riscv_ftrace_in_stop_machine = true;
}
void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
{
+ riscv_ftrace_in_stop_machine = false;
mutex_unlock(&text_mutex);
}
@@ -134,9 +145,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
int out;
- ftrace_arch_code_modify_prepare();
+ mutex_lock(&text_mutex);
out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
- ftrace_arch_code_modify_post_process();
+ mutex_unlock(&text_mutex);
return out;
}
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 765004b60513..56b70271518d 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -11,6 +11,7 @@
#include <asm/kprobes.h>
#include <asm/cacheflush.h>
#include <asm/fixmap.h>
+#include <asm/ftrace.h>
#include <asm/patch.h>
struct patch_insn {
@@ -59,8 +60,15 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
* Before reaching here, it was expected to lock the text_mutex
* already, so we don't need to give another lock here and could
* ensure that it was safe between each cores.
+ *
+ * We're currently using stop_machine() for ftrace, and while that
+ * ensures text_mutex is held before installing the mappings it does
+ * not ensure text_mutex is held by the calling thread. That's safe
+ * but triggers a lockdep failure, so just elide it for that specific
+ * case.
*/
- lockdep_assert_held(&text_mutex);
+ if (!riscv_ftrace_in_stop_machine)
+ lockdep_assert_held(&text_mutex);
if (across_pages)
patch_map(addr + len, FIX_TEXT_POKE1);
--
2.39.1
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^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-15 16:43 [PATCH v3] RISC-V: Don't check text_mutex during stop_machine Conor Dooley
@ 2023-02-16 11:31 ` Changbin Du
2023-02-24 11:07 ` Conor Dooley
0 siblings, 1 reply; 7+ messages in thread
From: Changbin Du @ 2023-02-16 11:31 UTC (permalink / raw
To: Conor Dooley
Cc: palmer, Palmer Dabbelt, linux-riscv, Steven Rostedt, Changbin Du,
Palmer Dabbelt, Conor Dooley, changbin.du
On Wed, Feb 15, 2023 at 04:43:17PM +0000, Conor Dooley wrote:
> From: Palmer Dabbelt <palmerdabbelt@google.com>
>
> We're currently using stop_machine() to update ftrace, which means that
> the thread that takes text_mutex during ftrace_prepare() may not be the
> same as the thread that eventually patches the code. This isn't
> actually a race because the lock is still held (preventing any other
> concurrent accesses) and there is only one thread running during
> stop_machine(), but it does trigger a lockdep failure.
>
> This patch just elides the lockdep check during stop_machine.
>
> Fixes: c15ac4fd60d5 ("riscv/ftrace: Add dynamic function tracer support")
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Reported-by: Changbin Du <changbin.du@gmail.com>
> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
> Resending this version as I am quite averse to deleting the assertion!
>
> Changes since v2 [<20220322022331.32136-1-palmer@rivosinc.com>]:
> * rebase on riscv/for-next as it as been a year.
> * incorporate Changbin's suggestion that init_nop should take the lock
> rather than call prepare() & post_process().
>
> Changes since v1 [<20210506071041.417854-1-palmer@dabbelt.com>]:
> * Use ftrace_arch_ocde_modify_{prepare,post_process}() to set the flag.
> I remember having a reason I wanted the function when I wrote the v1,
> but it's been almost a year and I forget what that was -- maybe I was
> just crazy, the patch was sent at midnight.
> * Fix DYNAMIC_FTRACE=n builds.
> ---
> arch/riscv/include/asm/ftrace.h | 7 +++++++
> arch/riscv/kernel/ftrace.c | 15 +++++++++++++--
> arch/riscv/kernel/patch.c | 10 +++++++++-
> 3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 04dad3380041..3ac7609f4ee9 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -81,8 +81,15 @@ do { \
> struct dyn_ftrace;
> int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
> #define ftrace_init_nop ftrace_init_nop
> +extern int riscv_ftrace_in_stop_machine;
> #endif
>
> +#else /* CONFIG_DYNAMIC_FTRACE */
> +
> +#ifndef __ASSEMBLY__
> +#define riscv_ftrace_in_stop_machine 0
> #endif
>
> +#endif /* CONFIG_DYNAMIC_FTRACE */
> +
> #endif /* _ASM_RISCV_FTRACE_H */
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 2086f6585773..661bfa72f359 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -11,14 +11,25 @@
> #include <asm/cacheflush.h>
> #include <asm/patch.h>
>
> +int riscv_ftrace_in_stop_machine;
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> {
> mutex_lock(&text_mutex);
> +
> + /*
> + * The code sequences we use for ftrace can't be patched while the
> + * kernel is running, so we need to use stop_machine() to modify them
> + * for now. This doesn't play nice with text_mutex, we use this flag
> + * to elide the check.
> + */
> + riscv_ftrace_in_stop_machine = true;
> }
>
> void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> {
> + riscv_ftrace_in_stop_machine = false;
> mutex_unlock(&text_mutex);
> }
>
> @@ -134,9 +145,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> {
> int out;
>
> - ftrace_arch_code_modify_prepare();
> + mutex_lock(&text_mutex);
> out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> - ftrace_arch_code_modify_post_process();
> + mutex_unlock(&text_mutex);
>
> return out;
> }
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 765004b60513..56b70271518d 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -11,6 +11,7 @@
> #include <asm/kprobes.h>
> #include <asm/cacheflush.h>
> #include <asm/fixmap.h>
> +#include <asm/ftrace.h>
> #include <asm/patch.h>
>
> struct patch_insn {
> @@ -59,8 +60,15 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
> * Before reaching here, it was expected to lock the text_mutex
> * already, so we don't need to give another lock here and could
> * ensure that it was safe between each cores.
> + *
> + * We're currently using stop_machine() for ftrace, and while that
> + * ensures text_mutex is held before installing the mappings it does
> + * not ensure text_mutex is held by the calling thread. That's safe
> + * but triggers a lockdep failure, so just elide it for that specific
> + * case.
> */
> - lockdep_assert_held(&text_mutex);
> + if (!riscv_ftrace_in_stop_machine)
> + lockdep_assert_held(&text_mutex);
>
> if (across_pages)
> patch_map(addr + len, FIX_TEXT_POKE1);
This misses this function.
int patch_text(void *addr, u32 insn)
{
struct patch_insn patch = {
.addr = addr,
.insn = insn,
.cpu_count = ATOMIC_INIT(0),
};
return stop_machine_cpuslocked(patch_text_cb,
&patch, cpu_online_mask);
}
> --
> 2.39.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
>
--
Cheers,
Changbin Du
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-16 11:31 ` Changbin Du
@ 2023-02-24 11:07 ` Conor Dooley
2023-02-24 12:58 ` Changbin Du
0 siblings, 1 reply; 7+ messages in thread
From: Conor Dooley @ 2023-02-24 11:07 UTC (permalink / raw
To: Changbin Du
Cc: Conor Dooley, palmer, Palmer Dabbelt, linux-riscv, Steven Rostedt,
Changbin Du, Palmer Dabbelt
[-- Attachment #1.1: Type: text/plain, Size: 7252 bytes --]
On Thu, Feb 16, 2023 at 07:31:26PM +0800, Changbin Du wrote:
> On Wed, Feb 15, 2023 at 04:43:17PM +0000, Conor Dooley wrote:
> > From: Palmer Dabbelt <palmerdabbelt@google.com>
> >
> > We're currently using stop_machine() to update ftrace, which means that
> > the thread that takes text_mutex during ftrace_prepare() may not be the
> > same as the thread that eventually patches the code. This isn't
> > actually a race because the lock is still held (preventing any other
> > concurrent accesses) and there is only one thread running during
> > stop_machine(), but it does trigger a lockdep failure.
> >
> > This patch just elides the lockdep check during stop_machine.
> >
> > Fixes: c15ac4fd60d5 ("riscv/ftrace: Add dynamic function tracer support")
> > Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> > Reported-by: Changbin Du <changbin.du@gmail.com>
> > Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
> > Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> > ---
> > Resending this version as I am quite averse to deleting the assertion!
> >
> > Changes since v2 [<20220322022331.32136-1-palmer@rivosinc.com>]:
> > * rebase on riscv/for-next as it as been a year.
> > * incorporate Changbin's suggestion that init_nop should take the lock
> > rather than call prepare() & post_process().
> >
> > Changes since v1 [<20210506071041.417854-1-palmer@dabbelt.com>]:
> > * Use ftrace_arch_ocde_modify_{prepare,post_process}() to set the flag.
> > I remember having a reason I wanted the function when I wrote the v1,
> > but it's been almost a year and I forget what that was -- maybe I was
> > just crazy, the patch was sent at midnight.
> > * Fix DYNAMIC_FTRACE=n builds.
> > ---
> > arch/riscv/include/asm/ftrace.h | 7 +++++++
> > arch/riscv/kernel/ftrace.c | 15 +++++++++++++--
> > arch/riscv/kernel/patch.c | 10 +++++++++-
> > 3 files changed, 29 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> > index 04dad3380041..3ac7609f4ee9 100644
> > --- a/arch/riscv/include/asm/ftrace.h
> > +++ b/arch/riscv/include/asm/ftrace.h
> > @@ -81,8 +81,15 @@ do { \
> > struct dyn_ftrace;
> > int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
> > #define ftrace_init_nop ftrace_init_nop
> > +extern int riscv_ftrace_in_stop_machine;
> > #endif
> >
> > +#else /* CONFIG_DYNAMIC_FTRACE */
> > +
> > +#ifndef __ASSEMBLY__
> > +#define riscv_ftrace_in_stop_machine 0
> > #endif
> >
> > +#endif /* CONFIG_DYNAMIC_FTRACE */
> > +
> > #endif /* _ASM_RISCV_FTRACE_H */
> > diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> > index 2086f6585773..661bfa72f359 100644
> > --- a/arch/riscv/kernel/ftrace.c
> > +++ b/arch/riscv/kernel/ftrace.c
> > @@ -11,14 +11,25 @@
> > #include <asm/cacheflush.h>
> > #include <asm/patch.h>
> >
> > +int riscv_ftrace_in_stop_machine;
> > +
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> > {
> > mutex_lock(&text_mutex);
> > +
> > + /*
> > + * The code sequences we use for ftrace can't be patched while the
> > + * kernel is running, so we need to use stop_machine() to modify them
> > + * for now. This doesn't play nice with text_mutex, we use this flag
> > + * to elide the check.
> > + */
> > + riscv_ftrace_in_stop_machine = true;
> > }
> >
> > void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> > {
> > + riscv_ftrace_in_stop_machine = false;
> > mutex_unlock(&text_mutex);
> > }
> >
> > @@ -134,9 +145,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> > {
> > int out;
> >
> > - ftrace_arch_code_modify_prepare();
> > + mutex_lock(&text_mutex);
> > out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> > - ftrace_arch_code_modify_post_process();
> > + mutex_unlock(&text_mutex);
> >
> > return out;
> > }
> > diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> > index 765004b60513..56b70271518d 100644
> > --- a/arch/riscv/kernel/patch.c
> > +++ b/arch/riscv/kernel/patch.c
> > @@ -11,6 +11,7 @@
> > #include <asm/kprobes.h>
> > #include <asm/cacheflush.h>
> > #include <asm/fixmap.h>
> > +#include <asm/ftrace.h>
> > #include <asm/patch.h>
> >
> > struct patch_insn {
> > @@ -59,8 +60,15 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
> > * Before reaching here, it was expected to lock the text_mutex
> > * already, so we don't need to give another lock here and could
> > * ensure that it was safe between each cores.
> > + *
> > + * We're currently using stop_machine() for ftrace, and while that
> > + * ensures text_mutex is held before installing the mappings it does
> > + * not ensure text_mutex is held by the calling thread. That's safe
> > + * but triggers a lockdep failure, so just elide it for that specific
> > + * case.
> > */
> > - lockdep_assert_held(&text_mutex);
> > + if (!riscv_ftrace_in_stop_machine)
> > + lockdep_assert_held(&text_mutex);
> >
> > if (across_pages)
> > patch_map(addr + len, FIX_TEXT_POKE1);
> This misses this function.
>
> int patch_text(void *addr, u32 insn)
So, with a corresponding rename to the symbol, does the following look
okay to you?
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index f21592d20306..433b454e693f 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -27,9 +27,15 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
p->ainsn.api.restore = (unsigned long)p->addr + offset;
+ /*
+ * kprobes takes text_mutex, but patch_text() calls stop_machine and
+ * lockdep gets confused by the context in which the lock is taken.
+ */
+ riscv_patch_in_stop_machine = true;
patch_text(p->ainsn.api.insn, p->opcode);
patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
__BUG_INSN_32);
+ riscv_patch_in_stop_machine = false;
}
static void __kprobes arch_prepare_simulate(struct kprobe *p)
@@ -96,16 +102,28 @@ void *alloc_insn_page(void)
/* install breakpoint in text */
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
+ /*
+ * kprobes takes text_mutex, but patch_text() calls stop_machine and
+ * lockdep gets confused by the context in which the lock is taken.
+ */
+ riscv_patch_in_stop_machine = true;
if ((p->opcode & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
patch_text(p->addr, __BUG_INSN_32);
else
patch_text(p->addr, __BUG_INSN_16);
+ riscv_patch_in_stop_machine = false;
}
/* remove breakpoint from text */
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
+ /*
+ * kprobes takes text_mutex, but patch_text() calls stop_machine and
+ * lockdep gets confused by the context in which the lock is taken.
+ */
+ riscv_patch_in_stop_machine = true;
patch_text(p->addr, p->opcode);
+ riscv_patch_in_stop_machine = false;
}
void __kprobes arch_remove_kprobe(struct kprobe *p)
[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]
[-- Attachment #2: Type: text/plain, Size: 161 bytes --]
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^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-24 11:07 ` Conor Dooley
@ 2023-02-24 12:58 ` Changbin Du
2023-02-24 13:46 ` Conor Dooley
0 siblings, 1 reply; 7+ messages in thread
From: Changbin Du @ 2023-02-24 12:58 UTC (permalink / raw
To: Conor Dooley
Cc: Changbin Du, Conor Dooley, palmer, Palmer Dabbelt, linux-riscv,
Steven Rostedt, Changbin Du, Palmer Dabbelt, Hui Wang
On Fri, Feb 24, 2023 at 11:07:42AM +0000, Conor Dooley wrote:
> > > - lockdep_assert_held(&text_mutex);
> > > + if (!riscv_ftrace_in_stop_machine)
> > > + lockdep_assert_held(&text_mutex);
> > >
> > > if (across_pages)
> > > patch_map(addr + len, FIX_TEXT_POKE1);
> > This misses this function.
> >
> > int patch_text(void *addr, u32 insn)
>
> So, with a corresponding rename to the symbol, does the following look
> okay to you?
>
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index f21592d20306..433b454e693f 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -27,9 +27,15 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>
> p->ainsn.api.restore = (unsigned long)p->addr + offset;
>
> + /*
> + * kprobes takes text_mutex, but patch_text() calls stop_machine and
> + * lockdep gets confused by the context in which the lock is taken.
> + */
> + riscv_patch_in_stop_machine = true;
> patch_text(p->ainsn.api.insn, p->opcode);
> patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
> __BUG_INSN_32);
> + riscv_patch_in_stop_machine = false;
> }
hmm, why not just put 'riscv_patch_in_stop_machine' into patch_text()? Then you
just need to modify that function.
--
Cheers,
Changbin Du
_______________________________________________
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-24 12:58 ` Changbin Du
@ 2023-02-24 13:46 ` Conor Dooley
2023-02-25 1:50 ` Changbin Du
0 siblings, 1 reply; 7+ messages in thread
From: Conor Dooley @ 2023-02-24 13:46 UTC (permalink / raw
To: Changbin Du
Cc: Conor Dooley, palmer, Palmer Dabbelt, linux-riscv, Steven Rostedt,
Changbin Du, Palmer Dabbelt, Hui Wang
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On Fri, Feb 24, 2023 at 08:58:57PM +0800, Changbin Du wrote:
> On Fri, Feb 24, 2023 at 11:07:42AM +0000, Conor Dooley wrote:
> > > > - lockdep_assert_held(&text_mutex);
> > > > + if (!riscv_ftrace_in_stop_machine)
> > > > + lockdep_assert_held(&text_mutex);
> > > >
> > > > if (across_pages)
> > > > patch_map(addr + len, FIX_TEXT_POKE1);
> > > This misses this function.
> > >
> > > int patch_text(void *addr, u32 insn)
> >
> > So, with a corresponding rename to the symbol, does the following look
> > okay to you?
> >
> > diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> > index f21592d20306..433b454e693f 100644
> > --- a/arch/riscv/kernel/probes/kprobes.c
> > +++ b/arch/riscv/kernel/probes/kprobes.c
> > @@ -27,9 +27,15 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
> >
> > p->ainsn.api.restore = (unsigned long)p->addr + offset;
> >
> > + /*
> > + * kprobes takes text_mutex, but patch_text() calls stop_machine and
> > + * lockdep gets confused by the context in which the lock is taken.
> > + */
> > + riscv_patch_in_stop_machine = true;
> > patch_text(p->ainsn.api.insn, p->opcode);
> > patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
> > __BUG_INSN_32);
> > + riscv_patch_in_stop_machine = false;
> > }
> hmm, why not just put 'riscv_patch_in_stop_machine' into patch_text()? Then you
> just need to modify that function.
Right, I intentionally didn't do that as `riscv_patch_in_stop_machine`
skips the lockdep check, which we only want to do for codepaths we know
the lock will be held for.
I didn't want to put it in patch_text() so if users of patch_text() that
do not take the lock are added, they will be caught.
I'm probably just erring on the paranoid/conservative side of things!
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-24 13:46 ` Conor Dooley
@ 2023-02-25 1:50 ` Changbin Du
2023-02-25 13:45 ` Conor Dooley
0 siblings, 1 reply; 7+ messages in thread
From: Changbin Du @ 2023-02-25 1:50 UTC (permalink / raw
To: Conor Dooley
Cc: Changbin Du, Conor Dooley, palmer, Palmer Dabbelt, linux-riscv,
Steven Rostedt, Changbin Du, Palmer Dabbelt, Hui Wang
On Fri, Feb 24, 2023 at 01:46:38PM +0000, Conor Dooley wrote:
> On Fri, Feb 24, 2023 at 08:58:57PM +0800, Changbin Du wrote:
> > On Fri, Feb 24, 2023 at 11:07:42AM +0000, Conor Dooley wrote:
> > > > > - lockdep_assert_held(&text_mutex);
> > > > > + if (!riscv_ftrace_in_stop_machine)
> > > > > + lockdep_assert_held(&text_mutex);
> > > > >
> > > > > if (across_pages)
> > > > > patch_map(addr + len, FIX_TEXT_POKE1);
> > > > This misses this function.
> > > >
> > > > int patch_text(void *addr, u32 insn)
> > >
> > > So, with a corresponding rename to the symbol, does the following look
> > > okay to you?
> > >
> > > diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> > > index f21592d20306..433b454e693f 100644
> > > --- a/arch/riscv/kernel/probes/kprobes.c
> > > +++ b/arch/riscv/kernel/probes/kprobes.c
> > > @@ -27,9 +27,15 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
> > >
> > > p->ainsn.api.restore = (unsigned long)p->addr + offset;
> > >
> > > + /*
> > > + * kprobes takes text_mutex, but patch_text() calls stop_machine and
> > > + * lockdep gets confused by the context in which the lock is taken.
> > > + */
> > > + riscv_patch_in_stop_machine = true;
> > > patch_text(p->ainsn.api.insn, p->opcode);
> > > patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
> > > __BUG_INSN_32);
> > > + riscv_patch_in_stop_machine = false;
> > > }
> > hmm, why not just put 'riscv_patch_in_stop_machine' into patch_text()? Then you
> > just need to modify that function.
>
> Right, I intentionally didn't do that as `riscv_patch_in_stop_machine`
> skips the lockdep check, which we only want to do for codepaths we know
> the lock will be held for.
> I didn't want to put it in patch_text() so if users of patch_text() that
> do not take the lock are added, they will be caught.
>
Understood your concern. Then how abount below instead of discrete changes?
int patch_text(void *addr, u32 insn)
{
+ int ret;
struct patch_insn patch = {
.addr = addr,
.insn = insn,
.cpu_count = ATOMIC_INIT(0),
};
- return stop_machine_cpuslocked(patch_text_cb,
+ lockdep_assert_held(&text_mutex);
+ riscv_patch_in_stop_machine = true
+ ret = stop_machine_cpuslocked(patch_text_cb,
&patch, cpu_online_mask);
+ riscv_patch_in_stop_machine = false;
+ return ret;
}
> I'm probably just erring on the paranoid/conservative side of things!
--
Cheers,
Changbin Du
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3] RISC-V: Don't check text_mutex during stop_machine
2023-02-25 1:50 ` Changbin Du
@ 2023-02-25 13:45 ` Conor Dooley
0 siblings, 0 replies; 7+ messages in thread
From: Conor Dooley @ 2023-02-25 13:45 UTC (permalink / raw
To: Changbin Du, Conor Dooley
Cc: palmer, Palmer Dabbelt, linux-riscv, Steven Rostedt, Changbin Du,
Palmer Dabbelt, Hui Wang
On 25 February 2023 01:50:14 GMT, Changbin Du <changbin.du@huawei.com> wrote:
>On Fri, Feb 24, 2023 at 01:46:38PM +0000, Conor Dooley wrote:
>> On Fri, Feb 24, 2023 at 08:58:57PM +0800, Changbin Du wrote:
>> > On Fri, Feb 24, 2023 at 11:07:42AM +0000, Conor Dooley wrote:
>> > > > > - lockdep_assert_held(&text_mutex);
>> > > > > + if (!riscv_ftrace_in_stop_machine)
>> > > > > + lockdep_assert_held(&text_mutex);
>> > > > >
>> > > > > if (across_pages)
>> > > > > patch_map(addr + len, FIX_TEXT_POKE1);
>> > > > This misses this function.
>> > > >
>> > > > int patch_text(void *addr, u32 insn)
>> > >
>> > > So, with a corresponding rename to the symbol, does the following look
>> > > okay to you?
>> > >
>> > > diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>> > > index f21592d20306..433b454e693f 100644
>> > > --- a/arch/riscv/kernel/probes/kprobes.c
>> > > +++ b/arch/riscv/kernel/probes/kprobes.c
>> > > @@ -27,9 +27,15 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>> > >
>> > > p->ainsn.api.restore = (unsigned long)p->addr + offset;
>> > >
>> > > + /*
>> > > + * kprobes takes text_mutex, but patch_text() calls stop_machine and
>> > > + * lockdep gets confused by the context in which the lock is taken.
>> > > + */
>> > > + riscv_patch_in_stop_machine = true;
>> > > patch_text(p->ainsn.api.insn, p->opcode);
>> > > patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
>> > > __BUG_INSN_32);
>> > > + riscv_patch_in_stop_machine = false;
>> > > }
>> > hmm, why not just put 'riscv_patch_in_stop_machine' into patch_text()? Then you
>> > just need to modify that function.
>>
>> Right, I intentionally didn't do that as `riscv_patch_in_stop_machine`
>> skips the lockdep check, which we only want to do for codepaths we know
>> the lock will be held for.
>> I didn't want to put it in patch_text() so if users of patch_text() that
>> do not take the lock are added, they will be caught.
>>
>Understood your concern. Then how abount below instead of discrete changes?
Seems fair enough to me, I'll respin Monday - had some hardware fail so out of action right now.
Thanks,
Conor.
>
>int patch_text(void *addr, u32 insn)
> {
>+ int ret;
> struct patch_insn patch = {
> .addr = addr,
> .insn = insn,
> .cpu_count = ATOMIC_INIT(0),
> };
>
>- return stop_machine_cpuslocked(patch_text_cb,
>+ lockdep_assert_held(&text_mutex);
>+ riscv_patch_in_stop_machine = true
>+ ret = stop_machine_cpuslocked(patch_text_cb,
> &patch, cpu_online_mask);
>+ riscv_patch_in_stop_machine = false;
>+ return ret;
> }
>
>> I'm probably just erring on the paranoid/conservative side of things!
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^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2023-02-25 13:45 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-02-15 16:43 [PATCH v3] RISC-V: Don't check text_mutex during stop_machine Conor Dooley
2023-02-16 11:31 ` Changbin Du
2023-02-24 11:07 ` Conor Dooley
2023-02-24 12:58 ` Changbin Du
2023-02-24 13:46 ` Conor Dooley
2023-02-25 1:50 ` Changbin Du
2023-02-25 13:45 ` Conor Dooley
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