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Message-ID: <CACi5LpNue+9GVafB-aYxhTNRWf6jbRk9O6Vq8BCQO3EHWrNnrw@mail.gmail.com>
Date: Mon, 27 May 2019 00:15:11 +0530
From: Bhupesh Sharma <bhsharma@...hat.com>
To: Kairui Song <kasong@...hat.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>,
"David S . Miller" <davem@...emloft.net>,
Eric Biederman <ebiederm@...ssion.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump
On Fri, May 24, 2019 at 6:25 PM Dave Young <dyoung@...hat.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@...hat.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@...hat.com>
Thanks,
Bhupesh
> Otherwise:
>
> Acked-by: Dave Young <dyoung@...hat.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
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