Re: [PATCH v7 1/4] powerpc/fadump: reduce memory consumption for capture kernel

Hari Bathini
2017-08-18T14:02:05Z

On Friday 18 August 2017 05:27 PM, Michal Suchánek wrote:
> On Fri, 18 Aug 2017 16:20:53 +0530
> Hari Bathini <hbathini@linux.vnet.ibm.com> wrote:
>
>> Hi Michal,
>>
>>
>> Thanks for the patches. I tried testing with the patches:
>>
>> [ 0.000000] fadump: Firmware-assisted dump is active.
>> [ 0.000000] fadump: Modifying command line to enforce the
>> additional parameters passed through 'fadump_extra_args='
>> [ 0.000000] fadump: Original command line:
>> BOOT_IMAGE=/vmlinux-4.13.0-rc1-bz155783+ root=/dev/mapper/rhel-root
>> ro crashkernel=2048M fadump=on fadump_reserve_mem=1024M
>> "fadump_extra_args=nr_cpus=1 numa=off udev.childern-max=2"
>> rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap
>> [ 0.000000] fadump: Modified command line:
>> BOOT_IMAGE=/vmlinux-4.13.0-rc1-bz155783+ root=/dev/mapper/rhel-root
>> ro crashkernel=2048M fadump=on fadump_reserve_mem=1024M
>> "fadump_extra_args nr_cpus=1 numa=off udev.childern-max=2"
>> rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap
>>
>> Looks like the quotes are retained not enforcing the parameters...
> Hello,
>
> You are passing an argument >>"fadump_extra_args<< - that is an
> argument containing a quote in the name. I did not test this scenario

Actually, this was not intentional..
I passed fadump_extra_args="nr_cpus=1 numa=off udev.childern-max=2"
through grub loader
but chosen/bootargs ended up having "fadump_extra_args=nr_cpus=1
numa=off udev.childern-max=2".
Need to check why that is..

Thanks
Hari

> assuming the argument name would not match in this case. It would
> probably not match if the quote was in the middle of the argument
> name but at the start it is skipped. Note that due to the requirement
> to remove quotes symmetrically which is added in the third patch this
> case does not break the commandline - it merely makes the arguments
> ineffective.
>
> The format suggested in the documentation is
>>> fadump_extra_args="nr_cpus=1 numa=off udev.childern-max=2"<< - that
> is quotes around the value. This format worked in my testing.
>
> Unfortunately, the format with quote before argument name would
> probably require another extra parameter to the callback to detect
> properly.
>
> Thanks
>
> Michal
>
>> I am yet to test the patches in other scenarios though..
>>
>>
>> Thanks
>>
>> Hari
>>
>>
>> On Friday 18 August 2017 01:44 AM, Michal Suchanek wrote:
>>> From: Hari Bathini <hbathini@linux.vnet.ibm.com>
>>>
>>> With fadump (dump capture) kernel booting like a regular kernel, it
>>> needs almost the same amount of memory to boot as the production
>>> kernel, which is unwarranted for a dump capture kernel. But with no
>>> option to disable some of the unnecessary subsystems in fadump
>>> kernel, that much memory is wasted on fadump, depriving the
>>> production kernel of that memory.
>>>
>>> Introduce kernel parameter 'fadump_extra_args=' that would take
>>> regular parameters as a space separated quoted string, to be
>>> enforced when fadump is active. This 'fadump_extra_args=' parameter
>>> can be leveraged to pass parameters like nr_cpus=1,
>>> cgroup_disable=memory and numa=off, to disable unwarranted
>>> resources/subsystems.
>>>
>>> Also, ensure the log "Firmware-assisted dump is active" is printed
>>> early in the boot process to put the subsequent fadump messages in
>>> context.
>>>
>>> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
>>> Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
>>> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
>>> ---
>>> Changes from v6:
>>> Correct and simplify quote handling. Ideally I would like to extend
>>> parse_args to give the length of the original quoted value to
>>> callback. However, parse_args removes at most one doubel-quote from
>>> the start and one from the end so that is easy to detect. Otherwise
>>> all other users will have to be updated to trash the new argument.
>>> ---
>>> arch/powerpc/include/asm/fadump.h | 2 +
>>> arch/powerpc/kernel/fadump.c | 109
>>> ++++++++++++++++++++++++++++++++++++--
>>> arch/powerpc/kernel/prom.c | 7 +++ 3 files changed, 115
>>> insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/fadump.h
>>> b/arch/powerpc/include/asm/fadump.h index
>>> ce88bbe1d809..98ae00943fb3 100644 ---
>>> a/arch/powerpc/include/asm/fadump.h +++
>>> b/arch/powerpc/include/asm/fadump.h @@ -208,11 +208,13 @@ extern
>>> int early_init_dt_scan_fw_dump(unsigned long node, const char
>>> *uname, int depth, void *data); extern int fadump_reserve_mem(void);
>>> extern int setup_fadump(void);
>>> +extern void enforce_fadump_extra_args(char *cmdline);
>>> extern int is_fadump_active(void);
>>> extern void crash_fadump(struct pt_regs *, const char *);
>>> extern void fadump_cleanup(void);
>>>
>>> #else /* CONFIG_FA_DUMP */
>>> +static inline void enforce_fadump_extra_args(char *cmdline) { }
>>> static inline int is_fadump_active(void) { return 0; }
>>> static inline void crash_fadump(struct pt_regs *regs, const char
>>> *str) { } #endif
>>> diff --git a/arch/powerpc/kernel/fadump.c
>>> b/arch/powerpc/kernel/fadump.c index dc0c49cfd90a..a1614d9b8a21
>>> 100644 --- a/arch/powerpc/kernel/fadump.c
>>> +++ b/arch/powerpc/kernel/fadump.c
>>> @@ -78,8 +78,10 @@ int __init early_init_dt_scan_fw_dump(unsigned
>>> long node,
>>> * dump data waiting for us.
>>> */
>>> fdm_active = of_get_flat_dt_prop(node, "ibm,kernel-dump",
>>> NULL);
>>> - if (fdm_active)
>>> + if (fdm_active) {
>>> + pr_info("Firmware-assisted dump is active.\n");
>>> fw_dump.dump_active = 1;
>>> + }
>>>
>>> /* Get the sizes required to store dump data for the
>>> firmware provided
>>> * dump sections.
>>> @@ -332,8 +334,11 @@ int __init fadump_reserve_mem(void)
>>> {
>>> unsigned long base, size, memory_boundary;
>>>
>>> - if (!fw_dump.fadump_enabled)
>>> + if (!fw_dump.fadump_enabled) {
>>> + if (fw_dump.dump_active)
>>> + pr_warn("Firmware-assisted dump was active
>>> but kernel booted with fadump disabled!\n"); return 0;
>>> + }
>>>
>>> if (!fw_dump.fadump_supported) {
>>> printk(KERN_INFO "Firmware-assisted dump is not
>>> supported on" @@ -373,7 +378,6 @@ int __init
>>> fadump_reserve_mem(void) memory_boundary = memblock_end_of_DRAM();
>>>
>>> if (fw_dump.dump_active) {
>>> - printk(KERN_INFO "Firmware-assisted dump is
>>> active.\n"); /*
>>> * If last boot has crashed then reserve all the
>>> memory
>>> * above boot_memory_size so that we don't touch
>>> it until @@ -460,6 +464,105 @@ static int __init
>>> early_fadump_reserve_mem(char *p) }
>>> early_param("fadump_reserve_mem", early_fadump_reserve_mem);
>>>
>>> +#define FADUMP_EXTRA_ARGS_PARAM "fadump_extra_args="
>>> +#define FADUMP_EXTRA_ARGS_LEN
>>> (strlen(FADUMP_EXTRA_ARGS_PARAM) - 1) +
>>> +struct param_info {
>>> + char *cmdline;
>>> + char *tmp_cmdline;
>>> + int shortening;
>>> +};
>>> +
>>> +static void __init fadump_update_params(struct param_info
>>> *param_info,
>>> + char *param, char *val)
>>> +{
>>> + ptrdiff_t param_offset = param - param_info->tmp_cmdline;
>>> + size_t vallen = val ? strlen(val) : 0;
>>> + char *tgt = param_info->cmdline + param_offset +
>>> + FADUMP_EXTRA_ARGS_LEN - param_info->shortening;
>>> + int shortening = 0;
>>> +
>>> + if (!val)
>>> + return;
>>> +
>>> + /* remove '=' */
>>> + *tgt++ = ' ';
>>> +
>>> + /* next_arg removes one leading and one trailing '"' */
>>> + if (*tgt == '"')
>>> + shortening += 1;
>>> + if (*(tgt + vallen + shortening) == '"')
>>> + shortening += 1;
>>> +
>>> + /* remove one leading and one trailing quote if both are
>>> present */
>>> + if ((val[0] == '"') && (val[vallen - 1] == '"')) {
>>> + shortening += 2;
>>> + vallen -= 2;
>>> + val++;
>>> + }
>>> +
>>> + /* some characters were removed - move the trailing part
>>> of cmdline */
>>> + if (shortening) {
>>> + char *src;
>>> +
>>> + strncpy(tgt, val, vallen);
>>> + tgt += vallen;
>>> + src = tgt + shortening;
>>> + memmove(tgt, src, strlen(src) + 1);
>>> + }
>>> +
>>> + param_info->shortening += shortening;
>>> +}
>>> +
>>> +/*
>>> + * Reworks command line parameters and splits 'fadump_extra_args='
>>> param
>>> + * to enforce the parameters passed through it
>>> + */
>>> +static int __init fadump_rework_cmdline_params(char *param, char
>>> *val,
>>> + const char *unused,
>>> void *arg) +{
>>> + struct param_info *param_info = (struct param_info *)arg;
>>> +
>>> + if (strncmp(param, FADUMP_EXTRA_ARGS_PARAM,
>>> + strlen(FADUMP_EXTRA_ARGS_PARAM) - 1))
>>> + return 0;
>>> +
>>> + fadump_update_params(param_info, param, val);
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +/*
>>> + * Replace every occurrence of 'fadump_extra_args="param1 param2
>>> param3"'
>>> + * in cmdline with 'fadump_extra_args param1 param2 param3' by
>>> stripping
>>> + * off '=' and quotes, if any. This ensures that the additional
>>> parameters
>>> + * passed with 'fadump_extra_args=' are enforced.
>>> + */
>>> +void __init enforce_fadump_extra_args(char *cmdline)
>>> +{
>>> + static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
>>> + static char init_cmdline[COMMAND_LINE_SIZE] __initdata;
>>> + struct param_info param_info;
>>> +
>>> + if (strstr(cmdline, FADUMP_EXTRA_ARGS_PARAM) == NULL)
>>> + return;
>>> +
>>> + pr_info("Modifying command line to enforce the additional
>>> parameters passed through 'fadump_extra_args='"); +
>>> + param_info.cmdline = cmdline;
>>> + param_info.tmp_cmdline = tmp_cmdline;
>>> + param_info.shortening = 0;
>>> +
>>> + strlcpy(init_cmdline, cmdline, COMMAND_LINE_SIZE);
>>> +
>>> + strlcpy(tmp_cmdline, cmdline, COMMAND_LINE_SIZE);
>>> + parse_args("fadump params", tmp_cmdline, NULL, 0, 0, 0,
>>> + &param_info,
>>> &fadump_rework_cmdline_params); +
>>> + pr_info("Original command line: %s\n", init_cmdline);
>>> + pr_info("Modified command line: %s\n", cmdline);
>>> +}
>>> +
>>> static int register_fw_dump(struct fadump_mem_struct *fdm)
>>> {
>>> int rc, err;
>>> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
>>> index f83056297441..2e6f40217266 100644
>>> --- a/arch/powerpc/kernel/prom.c
>>> +++ b/arch/powerpc/kernel/prom.c
>>> @@ -693,6 +693,13 @@ void __init early_init_devtree(void *params)
>>> of_scan_flat_dt(early_init_dt_scan_root, NULL);
>>> of_scan_flat_dt(early_init_dt_scan_memory_ppc, NULL);
>>>
>>> + /*
>>> + * Look for 'fadump_extra_args=' parameter and enfore the
>>> additional
>>> + * parameters passed to it if fadump is active.
>>> + */
>>> + if (is_fadump_active())
>>> + enforce_fadump_extra_args(boot_command_line);
>>> +
>>> parse_early_param();
>>>
>>> /* make sure we've parsed cmdline for mem= before this
>>> */