From patchwork Wed Feb 26 18:56:25 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yosry Ahmed X-Patchwork-Id: 868606 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C7D2C236A73 for ; Wed, 26 Feb 2025 18:56:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740596205; cv=none; b=H5dNP98EPbOIilk+UhdU3+BeMov+u4pdU8CPHKxbeuhfuXFmu9ivQtHdM+UzPagU1WNckpTDyNwlj9NzpQHhTOCqhSmTp8AA2M84M80PaVIvbRVPaMNBQJYEDeMkbcBEjdo4iiiEd3P2dZE70exB0pd3csX5AhkNcvdITJeWh50= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740596205; c=relaxed/simple; bh=BfvB7Ae2SjINcTkge75atqrzDzgDgJ2AfU3Icy8j8D0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=uZaZuKP9rYcHaqU0XqP7ZqFVpZ5o/GTd97IMrDvFYJHPuYU2n6RjYghsH6LKR0JNVQ5ckAeDlbvBtKhf101/dGbzECCJ0jQAZD+GuQ3TRzxLSUzjJqrKCR40jl2WMNawvM+CFKJHDRWyugd8qxwXxLYJrD0V1WCUO35UAMSoK5I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=YaNvZkTn; arc=none smtp.client-ip=91.218.175.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="YaNvZkTn" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1740596200; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=N8k5YcDw/4VVVoJt0g7ZtdcJRICdTIVq9GtV33GN43Q=; b=YaNvZkTnOHDLxyQIGgKvqM0HAojGOASBbcB6efdVyccFg/kHmuLMQSGnAfjxgT7154Nqss Gyq8YeI88LRUDOrnIYbtZGZGksf58O/nV3chzVwf2utfExIgizxXtT0eOVYUb2tGAAx4v/ 14L6ljsqjbvbLMdzmnP0hqDnEJvp+zg= From: Yosry Ahmed To: Andrew Morton Cc: Johannes Weiner , Nhat Pham , Chengming Zhou , "David S. Miller" , Herbert Xu , linux-mm@kvack.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Yosry Ahmed , syzbot+1a517ccfcbc6a7ab0f82@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: [PATCH v2] mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() Date: Wed, 26 Feb 2025 18:56:25 +0000 Message-ID: <20250226185625.2672936-1-yosry.ahmed@linux.dev> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Currently, zswap_cpu_comp_dead() calls crypto_free_acomp() while holding the per-CPU acomp_ctx mutex. crypto_free_acomp() then holds scomp_lock (through crypto_exit_scomp_ops_async()). On the other hand, crypto_alloc_acomp_node() holds the scomp_lock (through crypto_scomp_init_tfm()), and then allocates memory. If the allocation results in reclaim, we may attempt to hold the per-CPU acomp_ctx mutex. The above dependencies can cause an ABBA deadlock. For example in the following scenario: (1) Task A running on CPU #1: crypto_alloc_acomp_node() Holds scomp_lock Enters reclaim Reads per_cpu_ptr(pool->acomp_ctx, 1) (2) Task A is descheduled (3) CPU #1 goes offline zswap_cpu_comp_dead(CPU #1) Holds per_cpu_ptr(pool->acomp_ctx, 1)) Calls crypto_free_acomp() Waits for scomp_lock (4) Task A running on CPU #2: Waits for per_cpu_ptr(pool->acomp_ctx, 1) // Read on CPU #1 DEADLOCK Since there is no requirement to call crypto_free_acomp() with the per-CPU acomp_ctx mutex held in zswap_cpu_comp_dead(), move it after the mutex is unlocked. Also move the acomp_request_free() and kfree() calls for consistency and to avoid any potential sublte locking dependencies in the future. With this, only setting acomp_ctx fields to NULL occurs with the mutex held. This is similar to how zswap_cpu_comp_prepare() only initializes acomp_ctx fields with the mutex held, after performing all allocations before holding the mutex. Opportunistically, move the NULL check on acomp_ctx so that it takes place before the mutex dereference. Fixes: 12dcb0ef5406 ("mm: zswap: properly synchronize freeing resources during CPU hotunplug") Reported-by: syzbot+1a517ccfcbc6a7ab0f82@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67bcea51.050a0220.bbfd1.0096.GAE@google.com/ Cc: Co-developed-by: Herbert Xu Signed-off-by: Herbert Xu Signed-off-by: Yosry Ahmed Acked-by: Herbert Xu --- v1 -> v2: - Explained the problem more clearly in the commit message. - Moved all freeing calls outside the lock critical section. v1: https://lore.kernel.org/all/Z72FJnbA39zWh4zS@gondor.apana.org.au/ --- mm/zswap.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index ac9d299e7d0c1..adf745c66aa1d 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -881,18 +881,32 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node) { struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node); struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu); + struct acomp_req *req; + struct crypto_acomp *acomp; + u8 *buffer; + + if (IS_ERR_OR_NULL(acomp_ctx)) + return 0; mutex_lock(&acomp_ctx->mutex); - if (!IS_ERR_OR_NULL(acomp_ctx)) { - if (!IS_ERR_OR_NULL(acomp_ctx->req)) - acomp_request_free(acomp_ctx->req); - acomp_ctx->req = NULL; - if (!IS_ERR_OR_NULL(acomp_ctx->acomp)) - crypto_free_acomp(acomp_ctx->acomp); - kfree(acomp_ctx->buffer); - } + req = acomp_ctx->req; + acomp = acomp_ctx->acomp; + buffer = acomp_ctx->buffer; + acomp_ctx->req = NULL; + acomp_ctx->acomp = NULL; + acomp_ctx->buffer = NULL; mutex_unlock(&acomp_ctx->mutex); + /* + * Do the actual freeing after releasing the mutex to avoid subtle + * locking dependencies causing deadlocks. + */ + if (!IS_ERR_OR_NULL(req)) + acomp_request_free(req); + if (!IS_ERR_OR_NULL(acomp)) + crypto_free_acomp(acomp); + kfree(buffer); + return 0; }