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De Francesco" , lkp@lists.01.org, lkp@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Xu Subject: Re: [shmem] 7a7256d5f5: WARNING:possible_recursive_locking_detected Message-ID: References: <202210211215.9dc6efb5-yujie.liu@intel.com> <20221021133041.5811e1fb291eb6aaf122a59c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221021133041.5811e1fb291eb6aaf122a59c@linux-foundation.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666391764; a=rsa-sha256; cv=none; b=MWiFNR03BMb44nluE86k1qoSMapyl2ZDcToXPNxrNknKH9C6U5wa8ypCGesaOtyFs+6n4O ge0vx5nsB3yUkClHxwPUUqbM1C0NRCGwNgEILY45hD8/vdv8jHTtiws5hy2HBrsDv9tsHA OphMNC2BXjTUFlbH9qeQwo3aOmvF2b0= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=WzRZvhoi; spf=none (imf04.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666391764; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=jbA5d1lgaEXO+4QZTUA12B0RXm0tJuHDtZjIwatPzE8=; b=cIDOpQaYwsBn188In8/xaTL78ae8uqyU1ClHF9QCtqAFwKqatNkEpiTJRSWzZdzZMNdS0O bSLfiHOLNxZX0XJQVHYf9yKX3YxNaI7Ii1pknbmK2cHF6FRnwFt8MA4FAVjOl3xNpiAZEK RYwGztp5jB2008blP6lrm4MHImY621I= Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=WzRZvhoi; spf=none (imf04.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Stat-Signature: epedgfszn5y4g57f9edajar87dghftdg X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: E42FC4002D X-Rspam-User: X-HE-Tag: 1666391763-880446 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Oct 21, 2022 at 01:30:41PM -0700, Andrew Morton wrote: > On Fri, 21 Oct 2022 14:09:16 +0100 Matthew Wilcox wrote: > > > On Fri, Oct 21, 2022 at 12:10:17PM +0800, kernel test robot wrote: > > > FYI, we noticed WARNING:possible_recursive_locking_detected due to commit (built with gcc-11): > > > > > > commit: 7a7256d5f512b6c17957df7f59cf5e281b3ddba3 ("shmem: convert shmem_mfill_atomic_pte() to use a folio") > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > > > Ummm. Looks to me like this now occurs because of this part of the > > change: > > > > if (!zeropage) { /* COPY */ > > - page_kaddr = kmap_atomic(page); > > + page_kaddr = kmap_local_folio(folio, 0); > > ret = copy_from_user(page_kaddr, > > (const void __user *)src_addr, > > PAGE_SIZE); > > - kunmap_atomic(page_kaddr); > > + kunmap_local(page_kaddr); > > > > Should I be using __copy_from_user_inatomic() here? > > Caller __mcopy_atomic() is holding mmap_read_lock(dst_mm) and this > copy_from_user() calls > might_fault()->might_lock_read(current->mm->mmap_lock). > > And I guess might_lock_read() gets upset because we're holding another > mm's mmap_lock. Which sounds OK to me, unless a concurrent > mmap_write_lock() could jam things up. Well, are we sure that dst_mm and current->mm are necessarily different? If so, we could tell lockdep that. > But I cannot see why your patch would suddenly trigger this warning - > kmap_local_folio() and kmap_atomic() are basically the same thing. Except for the important call in kmap_atomic_prot() to pagefault_disable(). I mean, we could open-code that in the uffd code?