* [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-18 18:53 ` [PATCH 1/2] ARC: show_regs: avoid page allocator Vineet Gupta
@ 2018-12-18 18:53 ` Vineet Gupta
2018-12-19 17:04 ` Eugeniy Paltsev
` (2 subsequent siblings)
3 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-18 18:53 UTC (permalink / raw)
To: linux-snps-arc
Cc: linux-mm, linux-kernel, linux-arch, Peter Zijlstra, Vineet Gupta
Use on-stack smaller buffers instead of dynamic pages.
The motivation for this change was to address lockdep splat when
signal handling code calls show_regs (with preemption disabled) and
ARC show_regs calls into sleepable page allocator.
| potentially unexpected fatal signal 11.
| BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
| in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
| no locks held by segv/57.
| Preemption disabled at:
| [<8182f17e>] get_signal+0x4a6/0x7c4
| CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
|
| Stack Trace:
| arc_unwind_core.constprop.1+0xd0/0xf4
| __might_sleep+0x1f6/0x234
| __get_free_pages+0x174/0xca0
| show_regs+0x22/0x330
| get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
| do_signal+0x30/0x224
| resume_user_mode_begin+0x90/0xd8
Despite this, lockdep still barfs (see next change), but this patch
still has merit as in we use smaller/localized buffers now and there's
less instructoh trace to sift thru when debugging pesky issues.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
arch/arc/kernel/troubleshoot.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index e8d9fb452346..2885bec71fb8 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -58,11 +58,12 @@ static void show_callee_regs(struct callee_regs *cregs)
print_reg_file(&(cregs->r13), 13);
}
-static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
+static void print_task_path_n_nm(struct task_struct *tsk)
{
char *path_nm = NULL;
struct mm_struct *mm;
struct file *exe_file;
+ char buf[256];
mm = get_task_mm(tsk);
if (!mm)
@@ -80,10 +81,9 @@ static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
pr_info("Path: %s\n", !IS_ERR(path_nm) ? path_nm : "?");
}
-static void show_faulting_vma(unsigned long address, char *buf)
+static void show_faulting_vma(unsigned long address)
{
struct vm_area_struct *vma;
- char *nm = buf;
struct mm_struct *active_mm = current->active_mm;
/* can't use print_vma_addr() yet as it doesn't check for
@@ -96,8 +96,11 @@ static void show_faulting_vma(unsigned long address, char *buf)
* if the container VMA is not found
*/
if (vma && (vma->vm_start <= address)) {
+ char buf[256];
+ char *nm = "?";
+
if (vma->vm_file) {
- nm = file_path(vma->vm_file, buf, PAGE_SIZE - 1);
+ nm = file_path(vma->vm_file, buf, 256-1);
if (IS_ERR(nm))
nm = "?";
}
@@ -173,13 +176,8 @@ void show_regs(struct pt_regs *regs)
{
struct task_struct *tsk = current;
struct callee_regs *cregs;
- char *buf;
-
- buf = (char *)__get_free_page(GFP_KERNEL);
- if (!buf)
- return;
- print_task_path_n_nm(tsk, buf);
+ print_task_path_n_nm(tsk);
show_regs_print_info(KERN_INFO);
show_ecr_verbose(regs);
@@ -189,7 +187,7 @@ void show_regs(struct pt_regs *regs)
(void *)regs->blink, (void *)regs->ret);
if (user_mode(regs))
- show_faulting_vma(regs->ret, buf); /* faulting code, not data */
+ show_faulting_vma(regs->ret); /* faulting code, not data */
pr_info("[STAT32]: 0x%08lx", regs->status32);
@@ -221,8 +219,6 @@ void show_regs(struct pt_regs *regs)
cregs = (struct callee_regs *)current->thread.callee_reg;
if (cregs)
show_callee_regs(cregs);
-
- free_page((unsigned long)buf);
}
void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
--
2.7.4
^ permalink raw reply related [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-18 18:53 ` [PATCH 1/2] ARC: show_regs: avoid page allocator Vineet Gupta
2018-12-18 18:53 ` Vineet Gupta
@ 2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:04 ` Eugeniy Paltsev
` (2 more replies)
2018-12-19 20:46 ` William Kucharski
2018-12-20 12:57 ` Michal Hocko
3 siblings, 3 replies; 38+ messages in thread
From: Eugeniy Paltsev @ 2018-12-19 17:04 UTC (permalink / raw)
To: vineet.gupta1, linux-snps-arc; +Cc: linux-arch, linux-mm, peterz, linux-kernel
Hi Vineet,
Just curious: isn't that enough to use GFP_NOWAIT instead
of GFP_KERNEL when we allocate page in show_regs()?
As I can see x86 use print_vma_addr() in their show_signal_msg()
function which allocate page with __get_free_page(GFP_NOWAIT);
On Tue, 2018-12-18 at 10:53 -0800, Vineet Gupta wrote:
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> > potentially unexpected fatal signal 11.
> > BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> > in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> > no locks held by segv/57.
> > Preemption disabled at:
> > [<8182f17e>] get_signal+0x4a6/0x7c4
> > CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> >
> > Stack Trace:
> > arc_unwind_core.constprop.1+0xd0/0xf4
> > __might_sleep+0x1f6/0x234
> > __get_free_pages+0x174/0xca0
> > show_regs+0x22/0x330
> > get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> > do_signal+0x30/0x224
> > resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> ---
> arch/arc/kernel/troubleshoot.c | 22 +++++++++-------------
> 1 file changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
> index e8d9fb452346..2885bec71fb8 100644
> --- a/arch/arc/kernel/troubleshoot.c
> +++ b/arch/arc/kernel/troubleshoot.c
> @@ -58,11 +58,12 @@ static void show_callee_regs(struct callee_regs *cregs)
> print_reg_file(&(cregs->r13), 13);
> }
>
> -static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
> +static void print_task_path_n_nm(struct task_struct *tsk)
> {
> char *path_nm = NULL;
> struct mm_struct *mm;
> struct file *exe_file;
> + char buf[256];
>
> mm = get_task_mm(tsk);
> if (!mm)
> @@ -80,10 +81,9 @@ static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
> pr_info("Path: %s\n", !IS_ERR(path_nm) ? path_nm : "?");
> }
>
> -static void show_faulting_vma(unsigned long address, char *buf)
> +static void show_faulting_vma(unsigned long address)
> {
> struct vm_area_struct *vma;
> - char *nm = buf;
> struct mm_struct *active_mm = current->active_mm;
>
> /* can't use print_vma_addr() yet as it doesn't check for
> @@ -96,8 +96,11 @@ static void show_faulting_vma(unsigned long address, char *buf)
> * if the container VMA is not found
> */
> if (vma && (vma->vm_start <= address)) {
> + char buf[256];
> + char *nm = "?";
> +
> if (vma->vm_file) {
> - nm = file_path(vma->vm_file, buf, PAGE_SIZE - 1);
> + nm = file_path(vma->vm_file, buf, 256-1);
> if (IS_ERR(nm))
> nm = "?";
> }
> @@ -173,13 +176,8 @@ void show_regs(struct pt_regs *regs)
> {
> struct task_struct *tsk = current;
> struct callee_regs *cregs;
> - char *buf;
> -
> - buf = (char *)__get_free_page(GFP_KERNEL);
> - if (!buf)
> - return;
>
> - print_task_path_n_nm(tsk, buf);
> + print_task_path_n_nm(tsk);
> show_regs_print_info(KERN_INFO);
>
> show_ecr_verbose(regs);
> @@ -189,7 +187,7 @@ void show_regs(struct pt_regs *regs)
> (void *)regs->blink, (void *)regs->ret);
>
> if (user_mode(regs))
> - show_faulting_vma(regs->ret, buf); /* faulting code, not data */
> + show_faulting_vma(regs->ret); /* faulting code, not data */
>
> pr_info("[STAT32]: 0x%08lx", regs->status32);
>
> @@ -221,8 +219,6 @@ void show_regs(struct pt_regs *regs)
> cregs = (struct callee_regs *)current->thread.callee_reg;
> if (cregs)
> show_callee_regs(cregs);
> -
> - free_page((unsigned long)buf);
> }
>
> void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
--
Eugeniy Paltsev
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 17:04 ` Eugeniy Paltsev
@ 2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:36 ` Vineet Gupta
2018-12-20 1:16 ` Vineet Gupta
2 siblings, 0 replies; 38+ messages in thread
From: Eugeniy Paltsev @ 2018-12-19 17:04 UTC (permalink / raw)
To: vineet.gupta1, linux-snps-arc; +Cc: linux-arch, linux-mm, peterz, linux-kernel
Hi Vineet,
Just curious: isn't that enough to use GFP_NOWAIT instead
of GFP_KERNEL when we allocate page in show_regs()?
As I can see x86 use print_vma_addr() in their show_signal_msg()
function which allocate page with __get_free_page(GFP_NOWAIT);
On Tue, 2018-12-18 at 10:53 -0800, Vineet Gupta wrote:
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> > potentially unexpected fatal signal 11.
> > BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> > in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> > no locks held by segv/57.
> > Preemption disabled at:
> > [<8182f17e>] get_signal+0x4a6/0x7c4
> > CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> >
> > Stack Trace:
> > arc_unwind_core.constprop.1+0xd0/0xf4
> > __might_sleep+0x1f6/0x234
> > __get_free_pages+0x174/0xca0
> > show_regs+0x22/0x330
> > get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> > do_signal+0x30/0x224
> > resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> ---
> arch/arc/kernel/troubleshoot.c | 22 +++++++++-------------
> 1 file changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
> index e8d9fb452346..2885bec71fb8 100644
> --- a/arch/arc/kernel/troubleshoot.c
> +++ b/arch/arc/kernel/troubleshoot.c
> @@ -58,11 +58,12 @@ static void show_callee_regs(struct callee_regs *cregs)
> print_reg_file(&(cregs->r13), 13);
> }
>
> -static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
> +static void print_task_path_n_nm(struct task_struct *tsk)
> {
> char *path_nm = NULL;
> struct mm_struct *mm;
> struct file *exe_file;
> + char buf[256];
>
> mm = get_task_mm(tsk);
> if (!mm)
> @@ -80,10 +81,9 @@ static void print_task_path_n_nm(struct task_struct *tsk, char *buf)
> pr_info("Path: %s\n", !IS_ERR(path_nm) ? path_nm : "?");
> }
>
> -static void show_faulting_vma(unsigned long address, char *buf)
> +static void show_faulting_vma(unsigned long address)
> {
> struct vm_area_struct *vma;
> - char *nm = buf;
> struct mm_struct *active_mm = current->active_mm;
>
> /* can't use print_vma_addr() yet as it doesn't check for
> @@ -96,8 +96,11 @@ static void show_faulting_vma(unsigned long address, char *buf)
> * if the container VMA is not found
> */
> if (vma && (vma->vm_start <= address)) {
> + char buf[256];
> + char *nm = "?";
> +
> if (vma->vm_file) {
> - nm = file_path(vma->vm_file, buf, PAGE_SIZE - 1);
> + nm = file_path(vma->vm_file, buf, 256-1);
> if (IS_ERR(nm))
> nm = "?";
> }
> @@ -173,13 +176,8 @@ void show_regs(struct pt_regs *regs)
> {
> struct task_struct *tsk = current;
> struct callee_regs *cregs;
> - char *buf;
> -
> - buf = (char *)__get_free_page(GFP_KERNEL);
> - if (!buf)
> - return;
>
> - print_task_path_n_nm(tsk, buf);
> + print_task_path_n_nm(tsk);
> show_regs_print_info(KERN_INFO);
>
> show_ecr_verbose(regs);
> @@ -189,7 +187,7 @@ void show_regs(struct pt_regs *regs)
> (void *)regs->blink, (void *)regs->ret);
>
> if (user_mode(regs))
> - show_faulting_vma(regs->ret, buf); /* faulting code, not data */
> + show_faulting_vma(regs->ret); /* faulting code, not data */
>
> pr_info("[STAT32]: 0x%08lx", regs->status32);
>
> @@ -221,8 +219,6 @@ void show_regs(struct pt_regs *regs)
> cregs = (struct callee_regs *)current->thread.callee_reg;
> if (cregs)
> show_callee_regs(cregs);
> -
> - free_page((unsigned long)buf);
> }
>
> void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
--
Eugeniy Paltsev
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:04 ` Eugeniy Paltsev
@ 2018-12-19 17:36 ` Vineet Gupta
2018-12-19 17:36 ` Vineet Gupta
2018-12-20 1:16 ` Vineet Gupta
2 siblings, 1 reply; 38+ messages in thread
From: Vineet Gupta @ 2018-12-19 17:36 UTC (permalink / raw)
To: Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel
On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
> Just curious: isn't that enough to use GFP_NOWAIT instead
> of GFP_KERNEL when we allocate page in show_regs()?
>
> As I can see x86 use print_vma_addr() in their show_signal_msg()
> function which allocate page with __get_free_page(GFP_NOWAIT);
I'm not sure if lockdep will be happy with it still.
At any rate, as explained in changelog, this still has merit, since the buffer is
only needed for nested d_path calls, which are better served with a smaller
on-stack buffer. For cases such as kernel crash, we want lesser code/traces in
fault path to sift thru !
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 17:36 ` Vineet Gupta
@ 2018-12-19 17:36 ` Vineet Gupta
0 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-19 17:36 UTC (permalink / raw)
To: Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel
On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
> Just curious: isn't that enough to use GFP_NOWAIT instead
> of GFP_KERNEL when we allocate page in show_regs()?
>
> As I can see x86 use print_vma_addr() in their show_signal_msg()
> function which allocate page with __get_free_page(GFP_NOWAIT);
I'm not sure if lockdep will be happy with it still.
At any rate, as explained in changelog, this still has merit, since the buffer is
only needed for nested d_path calls, which are better served with a smaller
on-stack buffer. For cases such as kernel crash, we want lesser code/traces in
fault path to sift thru !
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:36 ` Vineet Gupta
@ 2018-12-20 1:16 ` Vineet Gupta
2018-12-20 1:16 ` Vineet Gupta
2018-12-20 13:30 ` Tetsuo Handa
2 siblings, 2 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 1:16 UTC (permalink / raw)
To: Eugeniy Paltsev, vineet.gupta1, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel
On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
> As I can see x86 use print_vma_addr() in their show_signal_msg()
> function which allocate page with __get_free_page(GFP_NOWAIT);
Indeed with that the __get_free_page() lockdep splat is gone.
There's a different one now hence my other patch.
| [ARCLinux]# ./segv-null-ptr
| potentially unexpected fatal signal 11.
| BUG: sleeping function called from invalid context at kernel/fork.c:1011
| in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
| no locks held by segv-null-ptr/70.
| CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
|
| Stack Trace:
| arc_unwind_core+0xcc/0x100
| ___might_sleep+0x17a/0x190
| mmput+0x16/0xb8
| show_regs+0x52/0x310
| get_signal+0x5ee/0x610
| do_signal+0x2c/0x218
| resume_user_mode_begin+0x90/0xd8
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 1:16 ` Vineet Gupta
@ 2018-12-20 1:16 ` Vineet Gupta
2018-12-20 13:30 ` Tetsuo Handa
1 sibling, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 1:16 UTC (permalink / raw)
To: Eugeniy Paltsev, vineet.gupta1, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel
On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
> As I can see x86 use print_vma_addr() in their show_signal_msg()
> function which allocate page with __get_free_page(GFP_NOWAIT);
Indeed with that the __get_free_page() lockdep splat is gone.
There's a different one now hence my other patch.
| [ARCLinux]# ./segv-null-ptr
| potentially unexpected fatal signal 11.
| BUG: sleeping function called from invalid context at kernel/fork.c:1011
| in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
| no locks held by segv-null-ptr/70.
| CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
|
| Stack Trace:
| arc_unwind_core+0xcc/0x100
| ___might_sleep+0x17a/0x190
| mmput+0x16/0xb8
| show_regs+0x52/0x310
| get_signal+0x5ee/0x610
| do_signal+0x2c/0x218
| resume_user_mode_begin+0x90/0xd8
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 1:16 ` Vineet Gupta
2018-12-20 1:16 ` Vineet Gupta
@ 2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 13:30 ` Tetsuo Handa
` (2 more replies)
1 sibling, 3 replies; 38+ messages in thread
From: Tetsuo Handa @ 2018-12-20 13:30 UTC (permalink / raw)
To: Vineet Gupta, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 2018/12/20 10:16, Vineet Gupta wrote:
> On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
>> As I can see x86 use print_vma_addr() in their show_signal_msg()
>> function which allocate page with __get_free_page(GFP_NOWAIT);
>
> Indeed with that the __get_free_page() lockdep splat is gone.
>
> There's a different one now hence my other patch.
>
> | [ARCLinux]# ./segv-null-ptr
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at kernel/fork.c:1011
> | in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
> | no locks held by segv-null-ptr/70.
> | CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
> |
> | Stack Trace:
> | arc_unwind_core+0xcc/0x100
> | ___might_sleep+0x17a/0x190
> | mmput+0x16/0xb8
Then, does mmput_async() help?
> | show_regs+0x52/0x310
> | get_signal+0x5ee/0x610
> | do_signal+0x2c/0x218
> | resume_user_mode_begin+0x90/0xd8
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 13:30 ` Tetsuo Handa
@ 2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 18:36 ` Vineet Gupta
2018-12-20 18:43 ` Vineet Gupta
2 siblings, 0 replies; 38+ messages in thread
From: Tetsuo Handa @ 2018-12-20 13:30 UTC (permalink / raw)
To: Vineet Gupta, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 2018/12/20 10:16, Vineet Gupta wrote:
> On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
>> As I can see x86 use print_vma_addr() in their show_signal_msg()
>> function which allocate page with __get_free_page(GFP_NOWAIT);
>
> Indeed with that the __get_free_page() lockdep splat is gone.
>
> There's a different one now hence my other patch.
>
> | [ARCLinux]# ./segv-null-ptr
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at kernel/fork.c:1011
> | in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
> | no locks held by segv-null-ptr/70.
> | CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
> |
> | Stack Trace:
> | arc_unwind_core+0xcc/0x100
> | ___might_sleep+0x17a/0x190
> | mmput+0x16/0xb8
Then, does mmput_async() help?
> | show_regs+0x52/0x310
> | get_signal+0x5ee/0x610
> | do_signal+0x2c/0x218
> | resume_user_mode_begin+0x90/0xd8
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 13:30 ` Tetsuo Handa
@ 2018-12-20 18:36 ` Vineet Gupta
2018-12-20 18:36 ` Vineet Gupta
2018-12-20 18:43 ` Vineet Gupta
2 siblings, 1 reply; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:36 UTC (permalink / raw)
To: Tetsuo Handa, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 12/20/18 5:30 AM, Tetsuo Handa wrote:
>> | mmput+0x16/0xb8
> Then, does mmput_async() help?
Probably, I can try.
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 18:36 ` Vineet Gupta
@ 2018-12-20 18:36 ` Vineet Gupta
0 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:36 UTC (permalink / raw)
To: Tetsuo Handa, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 12/20/18 5:30 AM, Tetsuo Handa wrote:
>> | mmput+0x16/0xb8
> Then, does mmput_async() help?
Probably, I can try.
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 18:36 ` Vineet Gupta
@ 2018-12-20 18:43 ` Vineet Gupta
2018-12-20 18:43 ` Vineet Gupta
2 siblings, 1 reply; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:43 UTC (permalink / raw)
To: Tetsuo Handa, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 12/20/18 5:30 AM, Tetsuo Handa wrote:
>> | Stack Trace:
>> | arc_unwind_core+0xcc/0x100
>> | ___might_sleep+0x17a/0x190
>> | mmput+0x16/0xb8
> Then, does mmput_async() help?
>
It helps, but then we get the next one (w/o my patch 2/2)
BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:23
in_atomic(): 1, irqs_disabled(): 0, pid: 69, name: segv-null-ptr
no locks held by segv-null-ptr/69.
CPU: 0 PID: 69 Comm: segv-null-ptr Not tainted 4.18.0+ #72
Stack Trace:
arc_unwind_core+0xcc/0x100
___might_sleep+0x17a/0x190
down_read+0x18/0x38
show_regs+0x102/0x310
get_signal+0x5ee/0x610
do_signal+0x2c/0x218
resume_user_mode_begin+0x90/0xd8
@off 0x103d4 in [/segv-null-pt
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 18:43 ` Vineet Gupta
@ 2018-12-20 18:43 ` Vineet Gupta
0 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:43 UTC (permalink / raw)
To: Tetsuo Handa, Eugeniy Paltsev, linux-snps-arc
Cc: linux-arch, linux-mm, peterz, linux-kernel, Michal Hocko
On 12/20/18 5:30 AM, Tetsuo Handa wrote:
>> | Stack Trace:
>> | arc_unwind_core+0xcc/0x100
>> | ___might_sleep+0x17a/0x190
>> | mmput+0x16/0xb8
> Then, does mmput_async() help?
>
It helps, but then we get the next one (w/o my patch 2/2)
BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:23
in_atomic(): 1, irqs_disabled(): 0, pid: 69, name: segv-null-ptr
no locks held by segv-null-ptr/69.
CPU: 0 PID: 69 Comm: segv-null-ptr Not tainted 4.18.0+ #72
Stack Trace:
arc_unwind_core+0xcc/0x100
___might_sleep+0x17a/0x190
down_read+0x18/0x38
show_regs+0x102/0x310
get_signal+0x5ee/0x610
do_signal+0x2c/0x218
resume_user_mode_begin+0x90/0xd8
@off 0x103d4 in [/segv-null-pt
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-18 18:53 ` [PATCH 1/2] ARC: show_regs: avoid page allocator Vineet Gupta
2018-12-18 18:53 ` Vineet Gupta
2018-12-19 17:04 ` Eugeniy Paltsev
@ 2018-12-19 20:46 ` William Kucharski
2018-12-19 20:46 ` William Kucharski
2018-12-19 21:36 ` Vineet Gupta
2018-12-20 12:57 ` Michal Hocko
3 siblings, 2 replies; 38+ messages in thread
From: William Kucharski @ 2018-12-19 20:46 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-arch, linux-mm, Peter Zijlstra, linux-snps-arc, linux-kernel
> On Dec 18, 2018, at 11:53 AM, Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:
>
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> | no locks held by segv/57.
> | Preemption disabled at:
> | [<8182f17e>] get_signal+0x4a6/0x7c4
> | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> |
> | Stack Trace:
> | arc_unwind_core.constprop.1+0xd0/0xf4
> | __might_sleep+0x1f6/0x234
> | __get_free_pages+0x174/0xca0
> | show_regs+0x22/0x330
> | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> | do_signal+0x30/0x224
> | resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
I would rather see 256 as a #define somewhere rather than a magic number sprinkled
around arch/arc/kernel/troubleshoot.c.
Still, that's what the existing code does, so I suppose it's OK.
Otherwise the change looks good.
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 20:46 ` William Kucharski
@ 2018-12-19 20:46 ` William Kucharski
2018-12-19 21:36 ` Vineet Gupta
1 sibling, 0 replies; 38+ messages in thread
From: William Kucharski @ 2018-12-19 20:46 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-snps-arc, linux-mm, linux-kernel, linux-arch, Peter Zijlstra
> On Dec 18, 2018, at 11:53 AM, Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:
>
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> | no locks held by segv/57.
> | Preemption disabled at:
> | [<8182f17e>] get_signal+0x4a6/0x7c4
> | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> |
> | Stack Trace:
> | arc_unwind_core.constprop.1+0xd0/0xf4
> | __might_sleep+0x1f6/0x234
> | __get_free_pages+0x174/0xca0
> | show_regs+0x22/0x330
> | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> | do_signal+0x30/0x224
> | resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
I would rather see 256 as a #define somewhere rather than a magic number sprinkled
around arch/arc/kernel/troubleshoot.c.
Still, that's what the existing code does, so I suppose it's OK.
Otherwise the change looks good.
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 20:46 ` William Kucharski
2018-12-19 20:46 ` William Kucharski
@ 2018-12-19 21:36 ` Vineet Gupta
2018-12-19 21:36 ` Vineet Gupta
1 sibling, 1 reply; 38+ messages in thread
From: Vineet Gupta @ 2018-12-19 21:36 UTC (permalink / raw)
To: William Kucharski
Cc: linux-arch, linux-mm, Peter Zijlstra, linux-snps-arc, linux-kernel
On 12/19/18 12:46 PM, William Kucharski wrote:
> I would rather see 256 as a #define somewhere rather than a magic number sprinkled
> around arch/arc/kernel/troubleshoot.c.
That bothered me as well, but I was too lazy to define one and the existing ones
don't apply. PATH_MAX is 4K which will blow up the stack usage.
>
> Still, that's what the existing code does, so I suppose it's OK.
I'll define one locally.
> Otherwise the change looks good.
Thx for taking a look.
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
I'll add this to the patch.
Thx,
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-19 21:36 ` Vineet Gupta
@ 2018-12-19 21:36 ` Vineet Gupta
0 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-19 21:36 UTC (permalink / raw)
To: William Kucharski
Cc: linux-arch, linux-mm, Peter Zijlstra, linux-snps-arc, linux-kernel
On 12/19/18 12:46 PM, William Kucharski wrote:
> I would rather see 256 as a #define somewhere rather than a magic number sprinkled
> around arch/arc/kernel/troubleshoot.c.
That bothered me as well, but I was too lazy to define one and the existing ones
don't apply. PATH_MAX is 4K which will blow up the stack usage.
>
> Still, that's what the existing code does, so I suppose it's OK.
I'll define one locally.
> Otherwise the change looks good.
Thx for taking a look.
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
I'll add this to the patch.
Thx,
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-18 18:53 ` [PATCH 1/2] ARC: show_regs: avoid page allocator Vineet Gupta
` (2 preceding siblings ...)
2018-12-19 20:46 ` William Kucharski
@ 2018-12-20 12:57 ` Michal Hocko
2018-12-20 12:57 ` Michal Hocko
2018-12-20 18:38 ` Vineet Gupta
3 siblings, 2 replies; 38+ messages in thread
From: Michal Hocko @ 2018-12-20 12:57 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-snps-arc, linux-mm, linux-kernel, linux-arch, Peter Zijlstra
On Tue 18-12-18 10:53:58, Vineet Gupta wrote:
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> | no locks held by segv/57.
> | Preemption disabled at:
> | [<8182f17e>] get_signal+0x4a6/0x7c4
> | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> |
> | Stack Trace:
> | arc_unwind_core.constprop.1+0xd0/0xf4
> | __might_sleep+0x1f6/0x234
> | __get_free_pages+0x174/0xca0
> | show_regs+0x22/0x330
> | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> | do_signal+0x30/0x224
> | resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
But show_regs is called from contexts which might be called from deep
call chains (e.g WARN). Is it safe to allocate such a large stack there?
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 12:57 ` Michal Hocko
@ 2018-12-20 12:57 ` Michal Hocko
2018-12-20 18:38 ` Vineet Gupta
1 sibling, 0 replies; 38+ messages in thread
From: Michal Hocko @ 2018-12-20 12:57 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-snps-arc, linux-mm, linux-kernel, linux-arch, Peter Zijlstra
On Tue 18-12-18 10:53:58, Vineet Gupta wrote:
> Use on-stack smaller buffers instead of dynamic pages.
>
> The motivation for this change was to address lockdep splat when
> signal handling code calls show_regs (with preemption disabled) and
> ARC show_regs calls into sleepable page allocator.
>
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317
> | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv
> | no locks held by segv/57.
> | Preemption disabled at:
> | [<8182f17e>] get_signal+0x4a6/0x7c4
> | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23
> |
> | Stack Trace:
> | arc_unwind_core.constprop.1+0xd0/0xf4
> | __might_sleep+0x1f6/0x234
> | __get_free_pages+0x174/0xca0
> | show_regs+0x22/0x330
> | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable()
> | do_signal+0x30/0x224
> | resume_user_mode_begin+0x90/0xd8
>
> Despite this, lockdep still barfs (see next change), but this patch
> still has merit as in we use smaller/localized buffers now and there's
> less instructoh trace to sift thru when debugging pesky issues.
But show_regs is called from contexts which might be called from deep
call chains (e.g WARN). Is it safe to allocate such a large stack there?
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 12:57 ` Michal Hocko
2018-12-20 12:57 ` Michal Hocko
@ 2018-12-20 18:38 ` Vineet Gupta
2018-12-20 18:38 ` Vineet Gupta
1 sibling, 1 reply; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:38 UTC (permalink / raw)
To: Michal Hocko
Cc: linux-snps-arc, linux-mm, linux-kernel, linux-arch, Peter Zijlstra
On 12/20/18 4:57 AM, Michal Hocko wrote:
>> Despite this, lockdep still barfs (see next change), but this patch
>> still has merit as in we use smaller/localized buffers now and there's
>> less instructoh trace to sift thru when debugging pesky issues.
> But show_regs is called from contexts which might be called from deep
> call chains (e.g WARN). Is it safe to allocate such a large stack there?
ARC has 8K pages and 256 additional bytes of stack usage doesn't seem absurdly
high to me !
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
2018-12-20 18:38 ` Vineet Gupta
@ 2018-12-20 18:38 ` Vineet Gupta
0 siblings, 0 replies; 38+ messages in thread
From: Vineet Gupta @ 2018-12-20 18:38 UTC (permalink / raw)
To: Michal Hocko
Cc: linux-snps-arc, linux-mm, linux-kernel, linux-arch, Peter Zijlstra
On 12/20/18 4:57 AM, Michal Hocko wrote:
>> Despite this, lockdep still barfs (see next change), but this patch
>> still has merit as in we use smaller/localized buffers now and there's
>> less instructoh trace to sift thru when debugging pesky issues.
> But show_regs is called from contexts which might be called from deep
> call chains (e.g WARN). Is it safe to allocate such a large stack there?
ARC has 8K pages and 256 additional bytes of stack usage doesn't seem absurdly
high to me !
-Vineet
^ permalink raw reply [flat|nested] 38+ messages in thread