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* [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
@ 2019-05-24  6:29 Kairui Song
  2019-05-24 12:54 ` Dave Young
  0 siblings, 1 reply; 5+ messages in thread
From: Kairui Song @ 2019-05-24  6:29 UTC (permalink / raw)
  To: linux-kernel
  Cc: Rahul Lakkireddy, David S . Miller, Eric Biederman,
	Alexey Dobriyan, Andrew Morton, Dave Young, kexec,
	Bhupesh Sharma, Kairui Song

Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
second kernel"), drivers is allowed to add device related dump data to
vmcore as they want by using the device dump API. This have a potential
issue, the data is stored in memory, drivers may append too much data
and use too much memory. The vmcore is typically used in a kdump kernel
which runs in a pre-reserved small chunk of memory. So as a result it
will make kdump unusable at all due to OOM issues.

So introduce new vmcore_device_dump= kernel parameter, and disable
device dump by default. User can enable it only if device dump data is
required for debugging, and have the chance to increase the kdump
reserved memory accordingly before device dump fails kdump.

Signed-off-by: Kairui Song <kasong@redhat.com>

---

 Update from V2:
  - Improve related docs

 Update from V1:
  - Use bool parameter to turn it on/off instead of letting user give
    the size limit. Size of device dump is hard to determine.

 Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
 fs/proc/Kconfig                                 |  6 ++++--
 fs/proc/vmcore.c                                | 13 +++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..3706ad9e1d97 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5078,6 +5078,20 @@
 			decrease the size and leave more room for directly
 			mapped kernel RAM.
 
+	vmcore_device_dump=	[KNL,KDUMP]
+			Format: {"off" | "on"}
+			Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
+			This parameter allows enable or disable device dump
+			for vmcore on kernel start-up.
+			Device dump allows drivers to append dump data to
+			vmcore so you can collect driver specified debug info.
+			Note that the drivers could append the data without
+			any limit, and the data is stored in memory, this may
+			bring a significant memory stress. If you want to turn
+			on this option, make sure you have reserved enough memory
+			with crashkernel= parameter.
+			default: off
+
 	vmcp_cma=nn[MG]	[KNL,S390]
 			Sets the memory size reserved for contiguous memory
 			allocations for the vmcp device driver.
diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 817c02b13b1d..1a7a38976bb0 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
 	  recovery kernel's initramfs to collect its underlying device
 	  snapshot.
 
-	  If you say Y here, the collected device dumps will be added
-	  as ELF notes to /proc/vmcore.
+	  If you say Y here, a new kernel parameter 'vmcore_device_dump'
+	  will be available. You can then enable device dump by passing
+	  'vmcore_device_dump=on' to kernel, the collected device dumps
+	  will be added as ELF notes to /proc/vmcore.
 
 config PROC_SYSCTL
 	bool "Sysctl support (/proc/sys)" if EXPERT
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 3fe90443c1bb..d1b608b0efad 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -53,6 +53,8 @@ static struct proc_dir_entry *proc_vmcore;
 /* Device Dump list and mutex to synchronize access to list */
 static LIST_HEAD(vmcoredd_list);
 static DEFINE_MUTEX(vmcoredd_mutex);
+
+static bool vmcoredd_enabled;
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 /* Device Dump Size */
@@ -1451,6 +1453,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
 	size_t data_size;
 	int ret;
 
+	if (!vmcoredd_enabled) {
+		pr_err_once("Device dump is disabled\n");
+		return -EINVAL;
+	}
+
 	if (!data || !strlen(data->dump_name) ||
 	    !data->vmcoredd_callback || !data->size)
 		return -EINVAL;
@@ -1502,6 +1509,12 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
 	return ret;
 }
 EXPORT_SYMBOL(vmcore_add_device_dump);
+
+static int __init vmcoredd_parse_cmdline(char *arg)
+{
+	return kstrtobool(arg, &vmcoredd_enabled);
+}
+__setup("vmcore_device_dump=", vmcoredd_parse_cmdline);
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 /* Free all dumps in vmcore device dump list */
-- 
2.21.0


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
  2019-05-24  6:29 [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump Kairui Song
@ 2019-05-24 12:54 ` Dave Young
  2019-05-26 18:45   ` Bhupesh Sharma
  0 siblings, 1 reply; 5+ messages in thread
From: Dave Young @ 2019-05-24 12:54 UTC (permalink / raw)
  To: Kairui Song
  Cc: linux-kernel, Rahul Lakkireddy, David S . Miller, Eric Biederman,
	Alexey Dobriyan, Andrew Morton, kexec, Bhupesh Sharma

On 05/24/19 at 02:29pm, Kairui Song wrote:
> Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
> second kernel"), drivers is allowed to add device related dump data to
> vmcore as they want by using the device dump API. This have a potential
> issue, the data is stored in memory, drivers may append too much data
> and use too much memory. The vmcore is typically used in a kdump kernel
> which runs in a pre-reserved small chunk of memory. So as a result it
> will make kdump unusable at all due to OOM issues.
> 
> So introduce new vmcore_device_dump= kernel parameter, and disable
> device dump by default. User can enable it only if device dump data is
> required for debugging, and have the chance to increase the kdump
> reserved memory accordingly before device dump fails kdump.
> 
> Signed-off-by: Kairui Song <kasong@redhat.com>
> 
> ---
> 
>  Update from V2:
>   - Improve related docs
> 
>  Update from V1:
>   - Use bool parameter to turn it on/off instead of letting user give
>     the size limit. Size of device dump is hard to determine.
> 
>  Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
>  fs/proc/Kconfig                                 |  6 ++++--
>  fs/proc/vmcore.c                                | 13 +++++++++++++
>  3 files changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 138f6664b2e2..3706ad9e1d97 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5078,6 +5078,20 @@
>  			decrease the size and leave more room for directly
>  			mapped kernel RAM.
>  
> +	vmcore_device_dump=	[KNL,KDUMP]
> +			Format: {"off" | "on"}
> +			Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
> +			This parameter allows enable or disable device dump
> +			for vmcore on kernel start-up.
> +			Device dump allows drivers to append dump data to
> +			vmcore so you can collect driver specified debug info.
> +			Note that the drivers could append the data without
> +			any limit, and the data is stored in memory, this may
> +			bring a significant memory stress. If you want to turn
> +			on this option, make sure you have reserved enough memory
> +			with crashkernel= parameter.
> +			default: off
> +
>  	vmcp_cma=nn[MG]	[KNL,S390]
>  			Sets the memory size reserved for contiguous memory
>  			allocations for the vmcp device driver.
> diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> index 817c02b13b1d..1a7a38976bb0 100644
> --- a/fs/proc/Kconfig
> +++ b/fs/proc/Kconfig
> @@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
>  	  recovery kernel's initramfs to collect its underlying device
>  	  snapshot.
>  
> -	  If you say Y here, the collected device dumps will be added
> -	  as ELF notes to /proc/vmcore.
> +	  If you say Y here, a new kernel parameter 'vmcore_device_dump'
> +	  will be available. You can then enable device dump by passing

"a new kernel parameter 'vmcore_device_dump' will be available" is not
necessary, "new" is a not a clear word.  I suggest to remove this
sentence.

s/You can then/You can

Otherwise:

Acked-by: Dave Young <dyoung@redhat.com>


> +	  'vmcore_device_dump=on' to kernel, the collected device dumps
> +	  will be added as ELF notes to /proc/vmcore.
>  
>  config PROC_SYSCTL
>  	bool "Sysctl support (/proc/sys)" if EXPERT
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 3fe90443c1bb..d1b608b0efad 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -53,6 +53,8 @@ static struct proc_dir_entry *proc_vmcore;
>  /* Device Dump list and mutex to synchronize access to list */
>  static LIST_HEAD(vmcoredd_list);
>  static DEFINE_MUTEX(vmcoredd_mutex);
> +
> +static bool vmcoredd_enabled;
>  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
>  
>  /* Device Dump Size */
> @@ -1451,6 +1453,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
>  	size_t data_size;
>  	int ret;
>  
> +	if (!vmcoredd_enabled) {
> +		pr_err_once("Device dump is disabled\n");
> +		return -EINVAL;
> +	}
> +
>  	if (!data || !strlen(data->dump_name) ||
>  	    !data->vmcoredd_callback || !data->size)
>  		return -EINVAL;
> @@ -1502,6 +1509,12 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
>  	return ret;
>  }
>  EXPORT_SYMBOL(vmcore_add_device_dump);
> +
> +static int __init vmcoredd_parse_cmdline(char *arg)
> +{
> +	return kstrtobool(arg, &vmcoredd_enabled);
> +}
> +__setup("vmcore_device_dump=", vmcoredd_parse_cmdline);
>  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
>  
>  /* Free all dumps in vmcore device dump list */
> -- 
> 2.21.0
> 

Thanks
Dave

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
  2019-05-24 12:54 ` Dave Young
@ 2019-05-26 18:45   ` Bhupesh Sharma
  2019-05-27  5:05     ` Kairui Song
  0 siblings, 1 reply; 5+ messages in thread
From: Bhupesh Sharma @ 2019-05-26 18:45 UTC (permalink / raw)
  To: Kairui Song
  Cc: Linux Kernel Mailing List, Rahul Lakkireddy, David S . Miller,
	Eric Biederman, Alexey Dobriyan, Andrew Morton, kexec,
	Dave Young

On Fri, May 24, 2019 at 6:25 PM Dave Young <dyoung@redhat.com> wrote:
>
> On 05/24/19 at 02:29pm, Kairui Song wrote:
> > Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
> > second kernel"), drivers is allowed to add device related dump data to
> > vmcore as they want by using the device dump API. This have a potential
> > issue, the data is stored in memory, drivers may append too much data
> > and use too much memory. The vmcore is typically used in a kdump kernel
> > which runs in a pre-reserved small chunk of memory. So as a result it
> > will make kdump unusable at all due to OOM issues.
> >
> > So introduce new vmcore_device_dump= kernel parameter, and disable
> > device dump by default. User can enable it only if device dump data is
> > required for debugging, and have the chance to increase the kdump
> > reserved memory accordingly before device dump fails kdump.
> >
> > Signed-off-by: Kairui Song <kasong@redhat.com>
> >
> > ---
> >
> >  Update from V2:
> >   - Improve related docs
> >
> >  Update from V1:
> >   - Use bool parameter to turn it on/off instead of letting user give
> >     the size limit. Size of device dump is hard to determine.
> >
> >  Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
> >  fs/proc/Kconfig                                 |  6 ++++--
> >  fs/proc/vmcore.c                                | 13 +++++++++++++
> >  3 files changed, 31 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 138f6664b2e2..3706ad9e1d97 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5078,6 +5078,20 @@
> >                       decrease the size and leave more room for directly
> >                       mapped kernel RAM.
> >
> > +     vmcore_device_dump=     [KNL,KDUMP]
> > +                     Format: {"off" | "on"}
> > +                     Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
> > +                     This parameter allows enable or disable device dump
> > +                     for vmcore on kernel start-up.
> > +                     Device dump allows drivers to append dump data to
> > +                     vmcore so you can collect driver specified debug info.
> > +                     Note that the drivers could append the data without
> > +                     any limit, and the data is stored in memory, this may
> > +                     bring a significant memory stress. If you want to turn
> > +                     on this option, make sure you have reserved enough memory
> > +                     with crashkernel= parameter.
> > +                     default: off
> > +
> >       vmcp_cma=nn[MG] [KNL,S390]
> >                       Sets the memory size reserved for contiguous memory
> >                       allocations for the vmcp device driver.
> > diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> > index 817c02b13b1d..1a7a38976bb0 100644
> > --- a/fs/proc/Kconfig
> > +++ b/fs/proc/Kconfig
> > @@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
> >         recovery kernel's initramfs to collect its underlying device
> >         snapshot.
> >
> > -       If you say Y here, the collected device dumps will be added
> > -       as ELF notes to /proc/vmcore.
> > +       If you say Y here, a new kernel parameter 'vmcore_device_dump'
> > +       will be available. You can then enable device dump by passing
>
> "a new kernel parameter 'vmcore_device_dump' will be available" is not
> necessary, "new" is a not a clear word.  I suggest to remove this
> sentence.
>
> s/You can then/You can

I agree with Dave. We are just trying to say here that even if
CONFIG_PROC_VMCORE_DEVICE_DUMP is set to Y, one can still disable the
device dump feature by passing parameter 'vmcore_device_dump=off' to
the kernel.

May be you can use the wording I mentioned in the v2 patch review,
which tried to convey a similar meaning.

With the change addressed:
Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>

Thanks,
Bhupesh


> Otherwise:
>
> Acked-by: Dave Young <dyoung@redhat.com>
>
>
> > +       'vmcore_device_dump=on' to kernel, the collected device dumps
> > +       will be added as ELF notes to /proc/vmcore.
> >
> >  config PROC_SYSCTL
> >       bool "Sysctl support (/proc/sys)" if EXPERT
> > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> > index 3fe90443c1bb..d1b608b0efad 100644
> > --- a/fs/proc/vmcore.c
> > +++ b/fs/proc/vmcore.c
> > @@ -53,6 +53,8 @@ static struct proc_dir_entry *proc_vmcore;
> >  /* Device Dump list and mutex to synchronize access to list */
> >  static LIST_HEAD(vmcoredd_list);
> >  static DEFINE_MUTEX(vmcoredd_mutex);
> > +
> > +static bool vmcoredd_enabled;
> >  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
> >
> >  /* Device Dump Size */
> > @@ -1451,6 +1453,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
> >       size_t data_size;
> >       int ret;
> >
> > +     if (!vmcoredd_enabled) {
> > +             pr_err_once("Device dump is disabled\n");
> > +             return -EINVAL;
> > +     }
> > +
> >       if (!data || !strlen(data->dump_name) ||
> >           !data->vmcoredd_callback || !data->size)
> >               return -EINVAL;
> > @@ -1502,6 +1509,12 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
> >       return ret;
> >  }
> >  EXPORT_SYMBOL(vmcore_add_device_dump);
> > +
> > +static int __init vmcoredd_parse_cmdline(char *arg)
> > +{
> > +     return kstrtobool(arg, &vmcoredd_enabled);
> > +}
> > +__setup("vmcore_device_dump=", vmcoredd_parse_cmdline);
> >  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
> >
> >  /* Free all dumps in vmcore device dump list */
> > --
> > 2.21.0
> >
>
> Thanks
> Dave

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
  2019-05-26 18:45   ` Bhupesh Sharma
@ 2019-05-27  5:05     ` Kairui Song
  2019-05-28  5:18       ` Dave Young
  0 siblings, 1 reply; 5+ messages in thread
From: Kairui Song @ 2019-05-27  5:05 UTC (permalink / raw)
  To: Bhupesh Sharma
  Cc: Linux Kernel Mailing List, Rahul Lakkireddy, David S . Miller,
	Eric Biederman, Alexey Dobriyan, Andrew Morton, kexec,
	Dave Young

On Mon, May 27, 2019 at 2:45 AM Bhupesh Sharma <bhsharma@redhat.com> wrote:
>
> On Fri, May 24, 2019 at 6:25 PM Dave Young <dyoung@redhat.com> wrote:
> >
> > On 05/24/19 at 02:29pm, Kairui Song wrote:
> > > Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
> > > second kernel"), drivers is allowed to add device related dump data to
> > > vmcore as they want by using the device dump API. This have a potential
> > > issue, the data is stored in memory, drivers may append too much data
> > > and use too much memory. The vmcore is typically used in a kdump kernel
> > > which runs in a pre-reserved small chunk of memory. So as a result it
> > > will make kdump unusable at all due to OOM issues.
> > >
> > > So introduce new vmcore_device_dump= kernel parameter, and disable
> > > device dump by default. User can enable it only if device dump data is
> > > required for debugging, and have the chance to increase the kdump
> > > reserved memory accordingly before device dump fails kdump.
> > >
> > > Signed-off-by: Kairui Song <kasong@redhat.com>
> > >
> > > ---
> > >
> > >  Update from V2:
> > >   - Improve related docs
> > >
> > >  Update from V1:
> > >   - Use bool parameter to turn it on/off instead of letting user give
> > >     the size limit. Size of device dump is hard to determine.
> > >
> > >  Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
> > >  fs/proc/Kconfig                                 |  6 ++++--
> > >  fs/proc/vmcore.c                                | 13 +++++++++++++
> > >  3 files changed, 31 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > index 138f6664b2e2..3706ad9e1d97 100644
> > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > @@ -5078,6 +5078,20 @@
> > >                       decrease the size and leave more room for directly
> > >                       mapped kernel RAM.
> > >
> > > +     vmcore_device_dump=     [KNL,KDUMP]
> > > +                     Format: {"off" | "on"}
> > > +                     Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
> > > +                     This parameter allows enable or disable device dump
> > > +                     for vmcore on kernel start-up.
> > > +                     Device dump allows drivers to append dump data to
> > > +                     vmcore so you can collect driver specified debug info.
> > > +                     Note that the drivers could append the data without
> > > +                     any limit, and the data is stored in memory, this may
> > > +                     bring a significant memory stress. If you want to turn
> > > +                     on this option, make sure you have reserved enough memory
> > > +                     with crashkernel= parameter.
> > > +                     default: off
> > > +
> > >       vmcp_cma=nn[MG] [KNL,S390]
> > >                       Sets the memory size reserved for contiguous memory
> > >                       allocations for the vmcp device driver.
> > > diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> > > index 817c02b13b1d..1a7a38976bb0 100644
> > > --- a/fs/proc/Kconfig
> > > +++ b/fs/proc/Kconfig
> > > @@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
> > >         recovery kernel's initramfs to collect its underlying device
> > >         snapshot.
> > >
> > > -       If you say Y here, the collected device dumps will be added
> > > -       as ELF notes to /proc/vmcore.
> > > +       If you say Y here, a new kernel parameter 'vmcore_device_dump'
> > > +       will be available. You can then enable device dump by passing
> >
> > "a new kernel parameter 'vmcore_device_dump' will be available" is not
> > necessary, "new" is a not a clear word.  I suggest to remove this
> > sentence.
> >
> > s/You can then/You can
>
> I agree with Dave. We are just trying to say here that even if
> CONFIG_PROC_VMCORE_DEVICE_DUMP is set to Y, one can still disable the
> device dump feature by passing parameter 'vmcore_device_dump=off' to
> the kernel.
>
> May be you can use the wording I mentioned in the v2 patch review,
> which tried to convey a similar meaning.
>
> With the change addressed:
> Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>
>
> Thanks,
> Bhupesh
>
OK, How about:

  If you say Y here, device dump is still disabled by default.
  You can enable device dump by passing 'vmcore_device_dump=on'
  to kernel, the collected device dumps will be added as ELF
  notes to /proc/vmcore.

If you think this is good I'll send V4 including the changes.

-- 
Best Regards,
Kairui Song

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
  2019-05-27  5:05     ` Kairui Song
@ 2019-05-28  5:18       ` Dave Young
  0 siblings, 0 replies; 5+ messages in thread
From: Dave Young @ 2019-05-28  5:18 UTC (permalink / raw)
  To: Kairui Song
  Cc: Bhupesh Sharma, Linux Kernel Mailing List, Rahul Lakkireddy,
	David S . Miller, Eric Biederman, Alexey Dobriyan, Andrew Morton,
	kexec

On 05/27/19 at 01:05pm, Kairui Song wrote:
> On Mon, May 27, 2019 at 2:45 AM Bhupesh Sharma <bhsharma@redhat.com> wrote:
> >
> > On Fri, May 24, 2019 at 6:25 PM Dave Young <dyoung@redhat.com> wrote:
> > >
> > > On 05/24/19 at 02:29pm, Kairui Song wrote:
> > > > Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
> > > > second kernel"), drivers is allowed to add device related dump data to
> > > > vmcore as they want by using the device dump API. This have a potential
> > > > issue, the data is stored in memory, drivers may append too much data
> > > > and use too much memory. The vmcore is typically used in a kdump kernel
> > > > which runs in a pre-reserved small chunk of memory. So as a result it
> > > > will make kdump unusable at all due to OOM issues.
> > > >
> > > > So introduce new vmcore_device_dump= kernel parameter, and disable
> > > > device dump by default. User can enable it only if device dump data is
> > > > required for debugging, and have the chance to increase the kdump
> > > > reserved memory accordingly before device dump fails kdump.
> > > >
> > > > Signed-off-by: Kairui Song <kasong@redhat.com>
> > > >
> > > > ---
> > > >
> > > >  Update from V2:
> > > >   - Improve related docs
> > > >
> > > >  Update from V1:
> > > >   - Use bool parameter to turn it on/off instead of letting user give
> > > >     the size limit. Size of device dump is hard to determine.
> > > >
> > > >  Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
> > > >  fs/proc/Kconfig                                 |  6 ++++--
> > > >  fs/proc/vmcore.c                                | 13 +++++++++++++
> > > >  3 files changed, 31 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > > index 138f6664b2e2..3706ad9e1d97 100644
> > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > @@ -5078,6 +5078,20 @@
> > > >                       decrease the size and leave more room for directly
> > > >                       mapped kernel RAM.
> > > >
> > > > +     vmcore_device_dump=     [KNL,KDUMP]
> > > > +                     Format: {"off" | "on"}
> > > > +                     Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
> > > > +                     This parameter allows enable or disable device dump
> > > > +                     for vmcore on kernel start-up.
> > > > +                     Device dump allows drivers to append dump data to
> > > > +                     vmcore so you can collect driver specified debug info.
> > > > +                     Note that the drivers could append the data without
> > > > +                     any limit, and the data is stored in memory, this may
> > > > +                     bring a significant memory stress. If you want to turn
> > > > +                     on this option, make sure you have reserved enough memory
> > > > +                     with crashkernel= parameter.
> > > > +                     default: off
> > > > +
> > > >       vmcp_cma=nn[MG] [KNL,S390]
> > > >                       Sets the memory size reserved for contiguous memory
> > > >                       allocations for the vmcp device driver.
> > > > diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> > > > index 817c02b13b1d..1a7a38976bb0 100644
> > > > --- a/fs/proc/Kconfig
> > > > +++ b/fs/proc/Kconfig
> > > > @@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
> > > >         recovery kernel's initramfs to collect its underlying device
> > > >         snapshot.
> > > >
> > > > -       If you say Y here, the collected device dumps will be added
> > > > -       as ELF notes to /proc/vmcore.
> > > > +       If you say Y here, a new kernel parameter 'vmcore_device_dump'
> > > > +       will be available. You can then enable device dump by passing
> > >
> > > "a new kernel parameter 'vmcore_device_dump' will be available" is not
> > > necessary, "new" is a not a clear word.  I suggest to remove this
> > > sentence.
> > >
> > > s/You can then/You can
> >
> > I agree with Dave. We are just trying to say here that even if
> > CONFIG_PROC_VMCORE_DEVICE_DUMP is set to Y, one can still disable the
> > device dump feature by passing parameter 'vmcore_device_dump=off' to
> > the kernel.
> >
> > May be you can use the wording I mentioned in the v2 patch review,
> > which tried to convey a similar meaning.
> >
> > With the change addressed:
> > Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>
> >
> > Thanks,
> > Bhupesh
> >
> OK, How about:
> 
>   If you say Y here, device dump is still disabled by default.
>   You can enable device dump by passing 'vmcore_device_dump=on'
>   to kernel, the collected device dumps will be added as ELF
>   notes to /proc/vmcore.
> 
> If you think this is good I'll send V4 including the changes.

Kairui, looks good.

rethink about it, to be even simple, just replace the __setup with core_param like
crash_kexec_post_notifiers, no need on/off. 

> 
> -- 
> Best Regards,
> Kairui Song

Thanks
Dave

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2019-05-28  5:18 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-24  6:29 [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump Kairui Song
2019-05-24 12:54 ` Dave Young
2019-05-26 18:45   ` Bhupesh Sharma
2019-05-27  5:05     ` Kairui Song
2019-05-28  5:18       ` Dave Young

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