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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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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> 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