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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 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 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 64B2540009 X-Stat-Signature: jrsfurg4e3ww8h9snmgwz1hjt6tz1aiz X-Rspam-User: X-HE-Tag: 1773910811-85251 X-HE-Meta: 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 hC/6Xh9y 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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