Commit bbb78b8f authored Sep 09, 2015 by Baoquan He Committed by Linus Torvalds Sep 10, 2015

kexec: align crash_notes allocation to make it be inside one physical page



People reported that crash_notes in /proc/vmcore were corrupted and this
cause crash kdump failure.  With code debugging and log we got the root
cause.  This is because percpu variable crash_notes are allocated in 2
vmalloc pages.  Currently percpu is based on vmalloc by default.  Vmalloc
can't guarantee 2 continuous vmalloc pages are also on 2 continuous
physical pages.  So when 1st kernel exports the starting address and size
of crash_notes through sysfs like below:

/sys/devices/system/cpu/cpux/crash_notes
/sys/devices/system/cpu/cpux/crash_notes_size

kdump kernel use them to get the content of crash_notes.  However the 2nd
part may not be in the next neighbouring physical page as we expected if
crash_notes are allocated accross 2 vmalloc pages.  That's why
nhdr_ptr->n_namesz or nhdr_ptr->n_descsz could be very huge in
update_note_header_size_elf64() and cause note header merging failure or
some warnings.

In this patch change to call __alloc_percpu() to passed in the align value
by rounding crash_notes_size up to the nearest power of two.  This makes
sure the crash_notes is allocated inside one physical page since
sizeof(note_buf_t) in all ARCHS is smaller than PAGE_SIZE.  Meanwhile add
a BUILD_BUG_ON to break compile if size is bigger than PAGE_SIZE since
crash_notes definitely will be in 2 pages.  That need be avoided, and need
be reported if it's unavoidable.

[akpm@linux-foundation.org: use correct comment layout]
Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Lisa Mitchell <lisa.mitchell@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 04e9949b

kernel/kexec_core.c

+22 −1

Original line number	Diff line number	Diff line
		@@ -1004,7 +1004,28 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
		static int __init crash_notes_memory_init(void)
		{
		/* Allocate memory for saving cpu registers. */
		crash_notes = alloc_percpu(note_buf_t);
		size_t size, align;

		/*
		* crash_notes could be allocated across 2 vmalloc pages when percpu
		* is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
		* pages are also on 2 continuous physical pages. In this case the
		* 2nd part of crash_notes in 2nd page could be lost since only the
		* starting address and size of crash_notes are exported through sysfs.
		* Here round up the size of crash_notes to the nearest power of two
		* and pass it to __alloc_percpu as align value. This can make sure
		* crash_notes is allocated inside one physical page.
		*/
		size = sizeof(note_buf_t);
		align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);

		/*
		* Break compile if size is bigger than PAGE_SIZE since crash_notes
		* definitely will be in 2 pages with that.
		*/
		BUILD_BUG_ON(size > PAGE_SIZE);

		crash_notes = __alloc_percpu(size, align);
		if (!crash_notes) {
		pr_warn("Kexec: Memory allocation for saving cpu register states failed\n");
		return -ENOMEM;

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