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 A68D130EF92 for ; Thu, 19 Mar 2026 09:00:10 +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=1773910810; cv=none; b=AtWAxNIoDsrvLZk8ZcdO0oJ6rNnPM2y5+2y15uHxJaW+VfTHv4Eh3ASTGrjrQEACnW/UhsVqg9xZffVz/DssmTzNhDMaVrPHbb40NC7Aw0U8nuJYLRKBzXLu0DPwvlKDr60HhJKPMha/HV/sWFPrb0rL/o0mYr5xZSTe3gL7cGM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773910810; c=relaxed/simple; bh=rutOn3YV5gTkK20mFe8/Y152SVFObowRGYBbVWX6jxo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uwacyDWqlv06Xz8w8Y4xryFHu+u5Y3d8o6cZN4APVpPhUFSLJJIlTe+SB7WUuFei9QJ8PGvSo+/tyjveCXnWQlabKhm9CAuzLo+zlyQJeVmAq+T7sVfyBHTpEMXXlE98gXHldIdInjTZP5/3USNiOE58pupmVH6cgHLf0le20Q8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=McPzNdsf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="McPzNdsf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 489E6C2BCAF; Thu, 19 Mar 2026 09:00:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773910810; bh=rutOn3YV5gTkK20mFe8/Y152SVFObowRGYBbVWX6jxo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=McPzNdsfk+0MOZqdYj77+2D1+dSQqQ0f5gUnODqByMZsfjluLsehrLlau5ZxvD3K2 SmjDZ/EBvi9YuZEKPeXbc7HUX4u9FPoYSH5LSk5PzAKVxmsArKSv6SEOTz86NODZo5 KVKmJnyHinzfH1vUYErfyY3XaCFnQFBIB12ulrfwsm/j6p7vsrcNZ2WOIBlBLrq41/ seQ/e3i2Y8+Wrx+5UGFH/J9uYW4+3gXccSGberHmrlXVIPgbezuU/KxiGpFu/GBPi/ iNOag5IvDofsp/QgyzdDzatWUDk1xTDDF6qbLOR5pLZuRReZDfr9fSzCwWPNS5qqx3 XP3jQr7OUR/wA== Message-ID: Date: Thu, 19 Mar 2026 10:00:00 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] kernel BUG in collapse_scan_file To: "Lorenzo Stoakes (Oracle)" , Lance Yang Cc: syzbot , willy@infradead.org, baolin.wang@linux.alibaba.com, npache@redhat.com, linux-mm@kvack.org, baohua@kernel.org, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, dev.jain@arm.com, ziy@nvidia.com, linux-kernel@vger.kernel.org, Liam.Howlett@oracle.com, akpm@linux-foundation.org References: <69bba3c0.050a0220.227207.002b.GAE@google.com> <10e5f1d6-077d-4783-aa16-6c8b98cb9e74@lucifer.local> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/19/26 09:53, Lorenzo Stoakes (Oracle) wrote: > On Thu, Mar 19, 2026 at 04:05:38PM +0800, Lance Yang wrote: >> Ccing Willy >> >> IIUC, this is a dup of the earlier report[1], which I looked into back >> in January. The root cause is the same: collapse_file() calls >> xas_lock_irq() without resetting the xas state first, tripping the >> XAS_INVALID() assertion: >> >> #define xas_lock_irq(xas) xa_lock_irq(XAS_INVALID(xas)->xa) >> >> static inline struct xa_state *XAS_INVALID(struct xa_state *xas) >> { >> XA_NODE_BUG_ON(xas->xa_node, xas_valid(xas)); >> return xas; >> } >> >> Added by commit: >> >> commit 43b00759f21b10142094d1ae5ff65cbb368953a3 >> Author: Matthew Wilcox (Oracle) >> Date: Sun Dec 14 10:53:31 2025 -0500 >> >> XArray: Add extra debugging check to xas_lock and friends >> >> While tracking down a recent bug, we discovered somewhere that had >> forgotten to call xas_reset() before calling xas_lock(). Add a debug >> check to be sure that doesn't happen in future and fix all the places in >> the test suite which were carelessly doing just this. >> >> Suggested-by: Linus Torvalds >> Signed-off-by: Matthew Wilcox (Oracle) >> >> I posted a HACK fix at the time[2], but David pointed out that Willy >> had mentioned it likely needs more thought[3]. > > Hmm we shouldn't leave this bug in place while working for a fancier fix?? > > Can we get _something_ going as an upstream fix? We can improve whatever we do > later right? > > David, thoughts? I recall Willy mentioning that the issue is likely a false positive. IIUC, that commit is not upstream? So it only triggers in linux-next. Which means: 1) If it's a false positive, upstream is not effected (no XA_NODE_BUG_ON) 2) If it's not a false positive, upstream is effected but does not trigger the XA_NODE_BUG_ON -- Cheers, David