kdump twirling - does not finish - commit 326e1b8f83a4318b09033ef754f40c785aed5e68

[Marshall Midden <marshallmidden@xxxxxxxxx>]

I know a translator is required - trying... Mark - is this better than typical?

Problem: kdump is not finishing, hangs twirling ... iKVM

Found: Power failure. Qlogic/Cavium/Marvell driver crash, but no kernel dump.  v5.3.8+local.

Reproduce: Boot, "echo c > /proc/sysrq-trigger"
Last known working release: v5.2.x (any of them).
First release failure: v5.3-rc1
Tried many versions up to v5.6-rc4 (2020-03-01).

Repository: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
System: Supermicro X10 dual socket x86_64, 64g/256g/512g (different systems/MB/CPUs).
UserLand: RedHat7.5
Tried (did not fix) kexec-tools fetched Feb 25th, 2020 from:
    git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
.config: No modules, except those listed below (only 10 "=m").
No modules in initramfs, /etc/dracut.conf.d/xxxx:
    omit_drivers+="qla2xxx nfs_layout_flexfiles"
    omit_drivers+=" tcm_loop tcm_fc target_core_mod iscsi_target_mod target_core_file"
    omit_drivers+=" target_core_iblock target_core_mod target_core_pscsi"

Commit where problem appeared (git bisect):
    commit 326e1b8f83a4318b09033ef754f40c785aed5e68
    Author: Dan Williams <dan.j.williams@xxxxxxxxx>
    Date:   Thu Jul 18 15:58:00 2019 -0700
------------------------------------------------------------------------------
-rw------- 1 root root 2174976 Feb 28 13:33 vmcore-incomplete
-rw-r--r-- 1 root root   87611 Feb 28 13:33 vmcore-dmesg.txt
verses
-rw------- 1 root root 1186929986 Mar  3 18:57 vmcore
-rw-r--r-- 1 root root     181709 Mar  3 18:57 vmcore-dmesg.txt
------------------------------------------------------------------------------
What am I breaking -- if I comment out the usage of early_section(ms)
in file mm/sparse.c -- although kdump's seems to work fine, etc.

//      bool section_is_early = early_section(ms);
...
//              if (!section_is_early) {
                        kfree(ms->usage);
                        ms->usage = NULL;
//              }

------------------------------------------------------------------------------
Humor:
    commit 5f9e832c137075045d15cd6899ab0505cfb2ca4b (tag: v5.3-rc1)
    Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
    Date:   Sun Jul 21 14:05:38 2019 -0700
        Linus 5.3-rc1
            ^
Horror:
    No one else has run into this since the end of July?

------------------------------------------------------------------------------

Full git show below:

commit 326e1b8f83a4318b09033ef754f40c785aed5e68
Author: Dan Williams <dan.j.williams@xxxxxxxxx>
Date:   Thu Jul 18 15:58:00 2019 -0700

    mm/sparsemem: introduce a SECTION_IS_EARLY flag

    In preparation for sub-section hotplug, track whether a given section
    was created during early memory initialization, or later via memory
    hotplug.  This distinction is needed to maintain the coarse expectation
    that pfn_valid() returns true for any pfn within a given section even if
    that section has pages that are reserved from the page allocator.

    For example one of the of goals of subsection hotplug is to support
    cases where the system physical memory layout collides System RAM and
    PMEM within a section.  Several pfn_valid() users expect to just check
    if a section is valid, but they are not careful to check if the given
    pfn is within a "System RAM" boundary and instead expect pgdat
    information to further validate the pfn.

    Rather than unwind those paths to make their pfn_valid() queries more
    precise a follow on patch uses the SECTION_IS_EARLY flag to maintain the
    traditional expectation that pfn_valid() returns true for all early
    sections.

    Link: https://lore.kernel.org/lkml/1560366952-10660-1-git-send-email-cai@xxxxxx/
    Link: http://lkml.kernel.org/r/156092350358.979959.5817209875548072819.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
    Reported-by: Qian Cai <cai@xxxxxx>
    Tested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>        [ppc64]
    Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
    Cc: Michal Hocko <mhocko@xxxxxxxx>
    Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
    Cc: David Hildenbrand <david@xxxxxxxxxx>
    Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
    Cc: Jane Chu <jane.chu@xxxxxxxxxx>
    Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
    Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
    Cc: Jonathan Corbet <corbet@xxxxxxx>
    Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
    Cc: Toshi Kani <toshi.kani@xxxxxxx>
    Cc: Vlastimil Babka <vbabka@xxxxxxx>
    Cc: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
    Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
    Cc: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2520336bdfd1..4be40634238b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1260,7 +1260,8 @@ extern size_t mem_section_usage_size(void);
 #define        SECTION_MARKED_PRESENT  (1UL<<0)
 #define SECTION_HAS_MEM_MAP    (1UL<<1)
 #define SECTION_IS_ONLINE      (1UL<<2)
-#define SECTION_MAP_LAST_BIT   (1UL<<3)
+#define SECTION_IS_EARLY       (1UL<<3)
+#define SECTION_MAP_LAST_BIT   (1UL<<4)
 #define SECTION_MAP_MASK       (~(SECTION_MAP_LAST_BIT-1))
 #define SECTION_NID_SHIFT      3

@@ -1286,6 +1287,11 @@ static inline int valid_section(struct mem_section *section)
        return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP));
 }

+static inline int early_section(struct mem_section *section)
+{
+       return (section && (section->section_mem_map & SECTION_IS_EARLY));
+}
+
 static inline int valid_section_nr(unsigned long nr)
 {
        return valid_section(__nr_to_section(nr));
diff --git a/mm/sparse.c b/mm/sparse.c
index 41bef8e1f65c..6d23a526279a 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -288,11 +288,11 @@ struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pn

 static void __meminit sparse_init_one_section(struct mem_section *ms,
                unsigned long pnum, struct page *mem_map,
-               struct mem_section_usage *usage)
+               struct mem_section_usage *usage, unsigned long flags)
 {
        ms->section_mem_map &= ~SECTION_MAP_MASK;
-       ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum) |
-                                                       SECTION_HAS_MEM_MAP;
+       ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum)
+               | SECTION_HAS_MEM_MAP | flags;
        ms->usage = usage;
 }

@@ -497,7 +497,8 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
                        goto failed;
                }
                check_usemap_section_nr(nid, usage);
-               sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage);
+               sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage,
+                               SECTION_IS_EARLY);
                usage = (void *) usage + mem_section_usage_size();
        }
        sparse_buffer_fini();
@@ -732,7 +733,7 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,

        set_section_nid(section_nr, nid);
        section_mark_present(ms);
-       sparse_init_one_section(ms, section_nr, memmap, usage);
+       sparse_init_one_section(ms, section_nr, memmap, usage, 0);

 out:
        if (ret < 0) {

@@ -772,19 +773,16 @@ static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
 }
 #endif

-static void free_section_usage(struct page *memmap,
+static void free_section_usage(struct mem_section *ms, struct page *memmap,
                struct mem_section_usage *usage, struct vmem_altmap *altmap)
 {
-       struct page *usage_page;
-
        if (!usage)
                return;

-       usage_page = virt_to_page(usage);
        /*
         * Check to see if allocation came from hot-plug-add
         */
-       if (PageSlab(usage_page) || PageCompound(usage_page)) {
+       if (!early_section(ms)) {
                kfree(usage);
                if (memmap)
                        __kfree_section_memmap(memmap, altmap);
@@ -816,6 +814,6 @@ void sparse_remove_one_section(struct mem_section *ms, unsigned long map_offset,

        clear_hwpoisoned_pages(memmap + map_offset,
                        PAGES_PER_SECTION - map_offset);
-       free_section_usage(memmap, usage, altmap);
+       free_section_usage(ms, memmap, usage, altmap);
 }
 #endif /* CONFIG_MEMORY_HOTPLUG */