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

Hari Bathini
2017-08-18T10:52:05Z

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...

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 */