From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 6815D9443; Fri, 21 Mar 2025 23:48:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742600901; cv=none; b=CnUOewfNvH80doe7KX+k4Frxdwt2ToNRP5wXL8R8g4NUyVqioJ3dLYwLpfAqzoFtcjuf/03eCQJt7kf0rOfHvPmdnU2R5Y3sAeyZ938DVLOzQz8rnJQrGqGBLNbqyO7l8bgMRcVqNCTZ5Qes7Oq64gL4wtKX4MlGYha1C1BKR/E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742600901; c=relaxed/simple; bh=JhRj1fKKbQQqevWhUjb4VVHtvgrGwS857rOw6WWcJWY=; h=Date:To:From:Subject:Message-Id; b=Po0/DpTDVx7GDGclUUURFD9mQSAz3TLhX5z0kosjoHJmgCKRbJn9b/Z8Gpjgo4d0Y6n3coyK9DrJgeelHD2sO9yjcTN6H3wPkp5TrLZ4P6gUiX2VIMHHrky87NLgx5L4+NeHZcO+HpaQn0FUMEAX/GhUeaAaiOMJZrx9vwY4zig= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=RfoOInar; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="RfoOInar" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B26ACC4CEE3; Fri, 21 Mar 2025 23:48:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1742600900; bh=JhRj1fKKbQQqevWhUjb4VVHtvgrGwS857rOw6WWcJWY=; h=Date:To:From:Subject:From; b=RfoOInarN0JT0InngPj+84sLP+9evhOgHDtTwiwxKHguQTL5QTYbg/ItXb6ZZyqjT YRQVyPe2IyoG3mIC9Z8s9I4viGNkbuRW+1ZwINoxcjVGPq3fTnlknp56XGr0hufid+ yXtE+OAEUsEVEv9GE2xwDnbZ+OI2onDWj7GdtgF8= Date: Fri, 21 Mar 2025 16:48:20 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,herbert@gondor.apana.org.au,hannes@cmpxchg.org,ebiggers@kernel.org,davem@davemloft.net,chengming.zhou@linux.dev,yosry.ahmed@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch added to mm-hotfixes-unstable branch Message-Id: <20250321234820.B26ACC4CEE3@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Yosry Ahmed Subject: mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() Date: Wed, 26 Feb 2025 18:56:25 +0000 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. Link: https://lkml.kernel.org/r/20250226185625.2672936-1-yosry.ahmed@linux.dev Fixes: 12dcb0ef5406 ("mm: zswap: properly synchronize freeing resources during CPU hotunplug") Signed-off-by: Herbert Xu Co-developed-by: Herbert Xu Signed-off-by: Yosry Ahmed Reported-by: syzbot+1a517ccfcbc6a7ab0f82@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67bcea51.050a0220.bbfd1.0096.GAE@google.com/ Acked-by: Herbert Xu Cc: Chengming Zhou Cc: David S. Miller Cc: Eric Biggers Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton --- mm/zswap.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) --- a/mm/zswap.c~mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead +++ a/mm/zswap.c @@ -881,18 +881,32 @@ static int zswap_cpu_comp_dead(unsigned { 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; } _ Patches currently in -mm which might be from yosry.ahmed@linux.dev are mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch