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David Hildenbrand aa05a044c5 vmw_balloon: indicate success when effectively deflating during migration 
[ Upstream commit 4ba5a8a7fa ]

When migrating a balloon page, we first deflate the old page to then
inflate the new page.

However, if inflating the new page succeeded, we effectively deflated the
old page, reducing the balloon size.

In that case, the migration actually worked: similar to migrating+
immediately deflating the new page.  The old page will be freed back to
the buddy.

Right now, the core will leave the page be marked as isolated (as we
returned an error).  When later trying to putback that page, we will run
into the WARN_ON_ONCE() in balloon_page_putback().

That handling was changed in commit 3544c4facc ("mm/balloon_compaction:
stop using __ClearPageMovable()"); before that change, we would have
tolerated that way of handling it.

To fix it, let's just return 0 in that case, making the core effectively
just clear the "isolated" flag + freeing it back to the buddy as if the
migration succeeded.  Note that the new page will also get freed when the
core puts the last reference.

Note that this also makes it all be more consistent: we will no longer
unisolate the page in the balloon driver while keeping it marked as being
isolated in migration core.

This was found by code inspection.

Link: https://lkml.kernel.org/r/20251014124455.478345-1-david@redhat.com
Fixes: 3544c4facc ("mm/balloon_compaction: stop using __ClearPageMovable()")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Jerrin Shaji George <jerrin.shaji-george@broadcom.com>
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-29 14:10:32 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.