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Mon, 26 Oct 2026 13:49:39 -0400 (EDT) Date: Mon, 26 Oct 2026 17:49:38 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 13/16] mm/shmem: preserve allocation errors when swapping in large entries Message-ID: References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-13-703206d5fa0c@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261026-fixes_shmem-v1-13-703206d5fa0c@kernel.org> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C2E30120004 X-Stat-Signature: w66n9c17gj7e6hccnbmzh55zw9oqabrk X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793036984-535775 X-HE-Meta: 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 vnvS6LmC GA1448BSC0p6DlFdhMGSjEzOCBexXkq5tTDSVokZvAM+7u+Xp5aZzAiIYD++0KUghAPUr033YIwhAeaf/5+nGN21aDPNkSLQmewjTNxmefViKVLjKemoq5a33/aE9qC0B14KrQij6ZtprkcrszUSDJCKbgbkJoIxDmu/9vPsPoLiqgtmioehnbkn+KYRJ/da5ffllyVQqPEA+31BESVpg+xE9NcoUG+zCIebdW9YJrJj8LPzV2jo80QW+PyPK8nBZfCTjhdRJOEzDWsHh1/1FPggrW7QDPLysNa3PHi3ED5itAOMsPJ8JImz0TVRvBdsZCeckRlDk1mz9FVJbcA8wgA1YGY+kUmO6JbF3xDoeP3uG4OC130GblQH+9ID892k/N0oSyXmIcyzgYuQAuQVZ4TicKkLn0eFxMj41qvYJlTKh+TSxGPU2SmAGhwEk+Eh+QWy+BK+Vw0v+jp3+p0O+nnbD5a5thMw/M/VbggOpcvHT0gXWcyoLoOp0H9ARd/Jd4pExY5umzpSI5MA4r1AAS1BCedTPG3SYo7uLH/VZnIQwvsdQTi0F85WgVXMBUxsPeLDyMUH9VzMoQEsLvYAAK6ulvyBUVTQmM3wFMvBPDXtXdI8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Oct 26, 2026 at 10:40:46AM +0100, David Hildenbrand (Arm) wrote: > shmem_swapin_folio() adjusts swap to the requested slot within a large > swap entry before allocating a folio. If allocation or charging fails, > the error path compares this adjusted value with the original entry > still stored in the XArray in shmem_confirm_swap(). > > Unless the index is at the start of the entry, this turns -ENOMEM into > -EEXIST even though nothing changed. > > The caller retries -EEXIST, so persistent allocation failures can leave > the task spinning instead of returning the error. > > Restore swap to index_entry on allocation failure so the existing error > path checks the original entry. This preserves the allocation error if > the entry is unchanged and still retries if it changed concurrently. > > Original fix generated by an LLM and sent by Josef Bacik in private. > > Fixes: 91ab656ece13 ("mm/shmem, swap: tidy up swap entry splitting") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) Acked-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov