From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793181431; b=Rmiab0b5B+4PjzvnHu5xLLlDmApPb4t/iKXarhecZ+83iEzSxzJGEnB7+Bu9Lt6bn3G+ W9sAOkXFo3ulHm/hgDla/9O7RRUSq4JCxZm+s6fLkW0LOozjdyQsBvHwopEfhH9liWofX tiWHO8VdVxRv5i5DkdaJKRwdHwbVN1KDdDC+16KMdlybKqCUToYSS+g9z7qipBDlZ2tVK V8os4UH58eUdT5Uj/ejxyzpdJYFYmeZkg1X5yHKYgqnnaopmeeski6vJXlaFAnkfbT3T2 8VVxfpNAj4d39IZpfe4xMXrJMe3vbxAXdXW78s81ZdqgudgpykanGKAkVhCQ7uUiR5g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793181431; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=u8v9MIEOd3AnLceYk8FQlKtEZ1PFUaFhFBv8xZI6BIQ=; b=V/4Iz+KwsqlA7LgbBaL6SKXFoKk9+uruKngkFxXlfaaRgx7DIIaq+5wusimCB4C577qa EeiC7XCQygMWeu7Smzu+wHSf0BJh5C9jVeGcv8ZQGKGGwoGb90181FkThyxD/zOJQvKz1 lJp/UocafIHhw+27DZhCyBBzYImKZjQXv6JVAWhwxl7j74BSs/gwZjwnJAi2Lo5AUddS6 B6JD7I6gfd/HpFdPm7R2pn6H2N188dkqSTdhAhnYyDIpI9DXrqozq0TB7aWiXLnwnn4Aw /+M2Jvaw4QncoZekD7nZoUSn+si05VcSzUNBhs0vvF5Wr6cplYtRyAnhec+3/Cgy8dg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=oTbgfszp; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2BE34606A31E; Wed, 28 Oct 2026 09:57:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=oTbgfszp Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FF851F01829; Wed, 28 Oct 2026 09:57:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793181431; bh=u8v9MIEOd3AnLceYk8FQlKtEZ1PFUaFhFBv8xZI6BIQ=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=oTbgfszppvM36lsf8lUjCiMv1vsa70dGrRu8OM7bDYQ6wcCUzbal4gTUW83Am4Rql bGXR2SdcuBjnhG4/z8cjriW/svQpXLJH3Zik5y0yyjXGH2j6jhE2MsS22JBS3BvE57 svpE4qka0BdvgfliwIkhdvWrSHAdy1Z8mBNIMpTAL8Co/nHh2BflN+SKGAO5hcJU7e FbsWFNTfzBA8ar+11+ZnO8ZM4vApyaRL8JQhiaurUgiVYN2wAUKHYvyVLTArAjstEF luY/fud/PGPk8yfhcqkn0OOsgUaPfUmcpT9tqmwdvFBNkpGHlp3jUuWQbNk0EomX8Q 6KbvBvcooJ7fg== From: "David Hildenbrand (Arm)" Date: Wed, 28 Oct 2026 10:55:12 +0100 Subject: [PATCH v3 14/15] mm/shmem: fix accounting of swapin-error markers 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="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261028-fixes_shmem-v3-14-4ce3baf2db4b@kernel.org> References: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> In-Reply-To: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> To: 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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , stable@vger.kernel.org X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4524; i=david@kernel.org; h=from:subject:message-id; bh=vZEz5P/rE8xLS5ut4sSBd9imyLTo+szC/Mtl6/SGSUc=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIeHmv+VDTntNSp/d84t1fc7lzZyJ+sXKuxscqn88KhZ 7Vyxf2eHaUsDGIcDLJiiixBwfcNXr5cV1vtxscMM4eVCWQIAxenAEyk5DLDP00r01mxTBZ1627q zNTdNz28Sjq31s7Gfd1mJhPrwHjuQwx/pdcvyr5aLeHlu/VbzMT/9YqPEv+lSOWIGqksvHbJWYu bGwA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A A failed swap read replaces the swap entry with a swapin-error marker in the page-cache and subtracts its pages from "alloced" and "swapped"; however, it leaves their block charge in place. Removing the marker during truncate then subtracts from "swapped" again. This can underflow the counters or make swapped reach zero while other pages remain swapped out, causing swapoff to loop without finding them. When installing the marker, subtract only from "swapped" and let shmem_recalc_inode() reduce "alloced" and release the block charge. Make shmem_free_swap() report successful removal separately from the number of swap pages freed, so removing a swapin-error marker does not subtract from "swapped" again. It's a bit confusing, but replacing a swapped out page by a swapin-error marker in shmem_set_folio_swapin_error() behaves as follows: Initially: alloced=1, swapped=1, nrpages=0 Calling shmem_recalc_inode(inode, 0, -1) -> swapped = 0 -> freed = 1 - 0 - 0 = 1 -> alloced -= freed -> alloced=0, swapped=0, block charge released Fixes: 6cec2b95dadf ("mm/shmem: fix infinite loop when swap in shmem error at swapoff time") Cc: stable@vger.kernel.org Tested-by: Gregory Price (Meta) Reviewed-by: Baolin Wang Signed-off-by: David Hildenbrand (Arm) --- mm/shmem.c | 31 ++++++++++++++----------------- 1 file changed, 14 insertions(+), 17 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 63f7fccf2ff5..11c3ac313c55 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1177,12 +1177,11 @@ static void shmem_delete_from_page_cache(struct folio *folio, void *radswap) } /* - * Remove swap entry from page cache, free the swap and its page cache. Returns - * the number of pages being freed. 0 means entry not found in XArray (0 pages - * being freed). + * Remove a swap entry or swapin-error marker wholly within [index, end]. + * Return whether it was removed, counting freed swap pages in nr_swaps_freed. */ -static long shmem_free_swap(struct address_space *mapping, - pgoff_t index, pgoff_t end, void *radswap) +static bool shmem_free_swap(struct address_space *mapping, + pgoff_t index, pgoff_t end, void *radswap, long *nr_swaps_freed) { XA_STATE(xas, &mapping->i_pages, index); const softleaf_t swp = radix_to_swp_entry(radswap); @@ -1203,8 +1202,10 @@ static long shmem_free_swap(struct address_space *mapping, xas_unlock_irq(&xas); /* A swapin-error marker holds no swap slot, so just drop it. */ - if (nr_pages && softleaf_is_swap(swp)) + if (nr_pages && softleaf_is_swap(swp)) { swap_put_entries_direct(swp, nr_pages); + *nr_swaps_freed += nr_pages; + } return nr_pages; } @@ -1358,8 +1359,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, if (xa_is_value(folio)) { if (unfalloc) continue; - nr_swaps_freed += shmem_free_swap(mapping, indices[i], - end - 1, folio); + shmem_free_swap(mapping, indices[i], end - 1, + folio, &nr_swaps_freed); continue; } @@ -1422,13 +1423,11 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, if (xa_is_value(folio)) { int order; - long swaps_freed; if (unfalloc) continue; - swaps_freed = shmem_free_swap(mapping, indices[i], - end - 1, folio); - if (!swaps_freed) { + if (!shmem_free_swap(mapping, indices[i], end - 1, + folio, &nr_swaps_freed)) { pgoff_t base = indices[i]; order = shmem_confirm_swap(mapping, indices[i], @@ -1449,7 +1448,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, index = base; break; } - nr_swaps_freed += swaps_freed; continue; } @@ -2409,11 +2407,10 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index, folio_put_swap(folio, NULL); swap_cache_del_folio(folio); /* - * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks - * won't be 0 when inode is released and thus trigger WARN_ON(i_blocks) - * in shmem_evict_inode(). + * Let shmem_recalc_inode() reduce alloced and release the block charge + * for the freed swap pages. */ - shmem_recalc_inode(inode, -nr_pages, -nr_pages); + shmem_recalc_inode(inode, 0, -nr_pages); } static int shmem_split_large_entry(struct inode *inode, pgoff_t index, -- 2.43.0