vmcore: add a kernel parameter novmcoredd

Since commit 2724273 ("vmcore: add API to collect hardware dump in
second kernel"), drivers are allowed to add device related dump data to
vmcore as they want by using the device dump API.  This has 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 'novmcoredd' command line option.  User can disable
device dump to reduce memory usage.  This is helpful if device dump is
using too much memory, disabling device dump could make sure a regular
vmcore without device dump data is still available.

[[email protected]: tweak documentation]
[[email protected]: vmcore.c needs moduleparam.h]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Kairui Song <[email protected]>
Acked-by: Dave Young <[email protected]>
Reviewed-by: Bhupesh Sharma <[email protected]>
Cc: Rahul Lakkireddy <[email protected]>
Cc: "David S . Miller" <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Baoquan He <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Documentation/admin-guide/kernel-parameters.txt

@@ -2877,6 +2877,17 @@
 			/sys/module/printk/parameters/console_suspend) to
 			turn on/off it dynamically.
 
+	novmcoredd	[KNL,KDUMP]
+			Disable device dump. Device dump allows drivers to
+			append dump data to vmcore so you can collect driver
+			specified debug info.  Drivers can append the data
+			without any limit and this data is stored in memory,
+			so this may cause significant memory stress.  Disabling
+			device dump can help save memory but the driver debug
+			data will be no longer available.  This parameter
+			is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
+			is set.
+
 	noaliencache	[MM, NUMA, SLAB] Disables the allocation of alien
 			caches in the slab allocator.  Saves per-node memory,
 			but will impact performance.

fs/proc/Kconfig

@@ -58,7 +58,8 @@ config PROC_VMCORE_DEVICE_DUMP
 	  snapshot.
 
 	  If you say Y here, the collected device dumps will be added
-	  as ELF notes to /proc/vmcore.
+	  as ELF notes to /proc/vmcore. You can still disable device
+	  dump using the kernel command line option 'novmcoredd'.
 
 config PROC_SYSCTL
 	bool "Sysctl support (/proc/sys)" if EXPERT

fs/proc/vmcore.c

@@ -21,6 +21,7 @@
 #include <linux/init.h>
 #include <linux/crash_dump.h>
 #include <linux/list.h>
+#include <linux/moduleparam.h>
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/pagemap.h>
@@ -54,6 +55,9 @@ 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_disabled;
+core_param(novmcoredd, vmcoredd_disabled, bool, 0);
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 /* Device Dump Size */
@@ -1452,6 +1456,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
 	size_t data_size;
 	int ret;
 
+	if (vmcoredd_disabled) {
+		pr_err_once("Device dump is disabled\n");
+		return -EINVAL;
+	}
+
 	if (!data || !strlen(data->dump_name) ||
 	    !data->vmcoredd_callback || !data->size)
 		return -EINVAL;