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=1793106306; b=NcIlBSHq+SEMxaEJNRXTo7F9d5y5RJSWPPp2ObfjyRybgpvD8hElHGouHLlbVdV71al+ KGvGo5gJM3oJ9sWgD833BmxdBUEqNTXqDMlGGnKTPeRVOEjbDHdhoG9sIJFs8y/dSlMwM 3wetPTiV9aTfwrbTwzJoQDsGFvtSEUaNevWTjN4mR9DsWV+CDMRLLNHcczA4sqynNNDLL 3AG+2/DdLLA6dYc9ISLpeoPUAlJqvshxVa1P1acFANDP69lugEJk2gVvGRzXmCkd2pWjJ ejDHrFaFRI2rnVDpdJEVFlNFWmZGPHwjzu28a5btBjgTiTGd+q7mvwRG956nhptWkZg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793106306; 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=bOndbVRJ8DlxLXPbni7eywyb2hjN3LJE2XVVvD2ZGUc=; b=aV574OUr2NlIVlNieQuWA8vGC1hW+o2TqHWwR8b2SKx29xfy1X+7vjNgIyi6MiK/esOc HyJG7x+fkpRIg34ZIOssUW/X/ParD3ZQyw+e1uTxTCT+j2a1aqeY384jB9ezAcrkOYXWv RqSFsDv8IcRlWs8e6yXXQJ+kCK+zKppI1ml6S28fx8jJ5smwjyZYvaExoHhy+VrGzQtOm UlxtHHuPnHgmZSsYj3O6GC0g12IIYYJ80B28KM5DaEqfJ6S9C8Lw+FyI2io1J1nNW3EIj gNkuj5KdIlWmnZlU7Gr8gVOQVzUYQvQBVpaq0YyPvBgLMoKZqYijy5hcOXX4rN8VKLA== 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=DRV+Jxka; 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 72FAC60A3804; Tue, 27 Oct 2026 13:05:06 +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=DRV+Jxka Received: by smtp.kernel.org (Postfix) with ESMTPSA id 659E11F031E2; Tue, 27 Oct 2026 13:04:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793106306; bh=bOndbVRJ8DlxLXPbni7eywyb2hjN3LJE2XVVvD2ZGUc=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=DRV+JxkaSnvJfTd5npTEX91RuHdUI+/15K4QT8r9upXL2PSDNr+9/jr34zrpahYG5 uN3UQsxink4uLO7qQ4uXsXtnNzrOx+xVfUtPE9TN1elqlki6KKd3LNlgVuBRgNO9Y1 szrO2Bo1P6qmCmlITy7JsrVG5+nc78XQ5u789Gs43D8axI80R8krX3gExauIf5m+Nh ev899EaswovRcIHaPeQwYbMNHYLiIXjgiFbgw9Ukbicpma2WlGazOCpqjUcGXU3djc 82MJ8wMfaKhNwpS35Y8+9cfWE5TxG3djF101jUGOg0Wr4a8OgBCjFaE/Q+E2x8O11U 49Dd7GOQptb1w== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 14:03:18 +0100 Subject: [PATCH v2 13/14] 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: <20261027-fixes_shmem-v2-13-86a00952acb9@kernel.org> References: <20261027-fixes_shmem-v2-0-86a00952acb9@kernel.org> In-Reply-To: <20261027-fixes_shmem-v2-0-86a00952acb9@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=4468; i=david@kernel.org; h=from:subject:message-id; bh=N6/aWIHU6WVoyGGH6bIqCWQy7AqZxJDPZKDhGMQWtQo=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIeLBSKNQ90tKu/r3eu7VHizHW2x47OTnYUvLPKXutbZ r7UthO+HaUsDGIcDLJiiixBwfcNXr5cV1vtxscMM4eVCWQIAxenAEwkmofhD++v+/K/SmULNX5p mTYGH5p7a03xqhX/vl7aY7HqX9auoIMM//3Ynz37ERa0VpbtDo9A5nKWpYW7MyzWFf574/BH9qX TOy4A 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) 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 4ece296a1ccf1..2800dbdf031c1 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; } @@ -2385,11 +2383,10 @@ 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