On Mon, Jan 25, 2021 at 10:01:48PM +0530, Naresh Kamboju wrote:

quoted

commit 8a3cc755b13808eba74846dfd1033fcbc21f9a65
Author: Al Viro [off-list ref]
Date:   Sun Mar 8 09:16:37 2020 -0400

    coredump: don't bother with do_truncate()

    have dump_skip() just remember how much needs to be skipped,
    leave actual seeks/writing zeroes to the next dump_emit()
    or the end of coredump output, whichever comes first.
    And instead of playing with do_truncate() in the end, just
    write one NUL at the end of the last gap (if any).

    Signed-off-by: Al Viro [off-list ref]

 fs/binfmt_elf.c          |  1 -
 fs/coredump.c            | 56 +++++++++++++++++++++++++++---------------------
 include/linux/binfmts.h  |  1 +
 include/linux/coredump.h |  1 -


Test case output link,
https://lkft.validation.linaro.org/scheduler/job/2184975#L1369
https://lkft.validation.linaro.org/scheduler/job/2184972#L1358

I think I see what's going on.  Could you check if the following
fixes your reproducer?

diff --git a/arch/powerpc/platforms/cell/spufs/coredump.c b/arch/powerpc/platforms/cell/spufs/coredump.c
index 60b5583e9eaf..1a587618015c 100644
--- a/arch/powerpc/platforms/cell/spufs/coredump.c
+++ b/arch/powerpc/platforms/cell/spufs/coredump.c

@@ -149,8 +149,7 @@ static int spufs_arch_write_note(struct spu_context *ctx, int i,
                        return -EIO;
        }

-       if (!dump_skip(cprm, roundup(cprm->pos - ret + sz, 4) - cprm->pos))
-               return -EIO;
+       dump_skip_to(cprm, roundup(cprm->pos - ret + sz, 4));
        return 0;
 }

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 66137d5dca5f..474a3c7dd5ce 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c

@@ -2267,8 +2267,7 @@ static int elf_core_dump(struct coredump_params *cprm)
                goto end_coredump;

        /* Align to page */
-       if (!dump_skip(cprm, dataoff - cprm->pos))
-               goto end_coredump;
+       dump_skip_to(cprm, dataoff);

        for (i = 0; i < vma_count; i++) {
                struct core_vma_metadata *meta = vma_meta + i;

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index be4062b8ba75..01f043971644 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c

@@ -1640,8 +1640,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
                                goto end_coredump;
        }

-       if (!dump_skip(cprm, dataoff - cprm->pos))
-               goto end_coredump;
+       dump_skip_to(cprm, dataoff);

        if (!elf_fdpic_dump_segments(cprm, vma_meta, vma_count))
                goto end_coredump;

diff --git a/fs/coredump.c b/fs/coredump.c
index 27a93f724251..bfac7422cd14 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c

@@ -894,7 +894,14 @@ int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 }
 EXPORT_SYMBOL(dump_emit);

-int dump_skip(struct coredump_params *cprm, size_t nr)
+void dump_skip_to(struct coredump_params *cprm, unsigned long pos)
+{
+       cprm->to_skip = pos - cprm->pos;
+       return 0;