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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sEexu-0000000FFDM-0FOy; Wed, 05 Jun 2024 00:57:22 +0000 Date: Wed, 5 Jun 2024 01:57:21 +0100 From: Matthew Wilcox To: Andrii Nakryiko Cc: linux-fsdevel@vger.kernel.org, brauner@kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, gregkh@linuxfoundation.org, linux-mm@kvack.org, liam.howlett@oracle.com, surenb@google.com, rppt@kernel.org Subject: Re: [PATCH v3 1/9] mm: add find_vma()-like API but RCU protected and taking VMA lock Message-ID: References: <20240605002459.4091285-1-andrii@kernel.org> <20240605002459.4091285-2-andrii@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240605002459.4091285-2-andrii@kernel.org> X-Rspam-User: X-Stat-Signature: a4ojtc1hy8xruzmsi36sfhsw43ehjfrk X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4D5F11C0003 X-HE-Tag: 1717549047-924235 X-HE-Meta: U2FsdGVkX1+zhF9UmvZnSOWhufWbQA1tEBdmuTa7NvgPge159fqtUdgW40Eqz/k5xz67g9B5Es9bTcENKkRfrj319rrVkUr3gewrr/OyddpDnVNabm9MzL7wIH95+tREkebMR56qqn6mzpCzMIh2m/B7+iPYQouK64trsYl6DxSPmCpk1e0o9WfZhqO0TsdR1V2YJ6jxtInDHkjeoPyZkI9WD5wo7kt5SS/WS5piSKfcLMBZqDdicGE6HqoAtCqhQzUObO7LEEzE+PYTXLkR+5ZFoEZEycD+PpIrBY7ojjPfMlUqb2ubCaHKbl1oRYYigITem+O9P5DzBvG1Ms+uqd+igzJFFdlzVOMxT4iNO1QtbiWPu8U7uLsWY1E94cJCPBxhOigcqa02zfj5vaHD1ILWLwpHaZFfobMfu7Hvw0iR8JjRSkS/5vgiVB/7/3boBOJiPThYEpwBUZr9+mlnwCAMWyw+4CYwXqBCkIdvydpIew7UANmgsaYO0astqLdCDIHZs/O+eOm94tvHaFG9bBzwK8tfYHUqJNctLZg7Oi/EK9ycpa/gggcQ2MADgg+pYSuwpalSEZeFz2eoddmi2DGbpCziCVIwvfDh38jTM1NmzQ1Zwzs1Yv9duPX4WrhWEiGPaZlaOrHC0wy2qJ4bDz+SS+aQsqyTZ+EDu7xnAy1UXpcO/6zcT+dGijUFi7SOwmlW2nsXOFp6RifbqljGXx0mXiIqSXrkvIwlpPqeL6OYiSFSD65ba74R9dxTWtK92r8qb6oJRVAiR6GcrxGUKuD/6SSlEcD+2VGm606IOw23sn+b369zWdskAH5zGEVn9HX+qekxMzpLnKyN7qxCL1qhQUXbxV5lgYzLYY8e5CUy02l/7zKLpyDr91ul1UR8Gw4/9lltv1CwvTv3+AlawQnrJgLvgbKdLG2vXoAROl6xSu0deykBgkCNs9uXluAS2vs/CkX4ZxDNp9a4UN6 spbsJ3rq NRF/2oh9dufNad3xtmhS+uWz1Q79ohzmv+vBVdWqRSh/MCtzrrJifL0ahUfSdexUqY6IUz8l7ecabZ/nXLZshHhIRLGhq0mNJRJ7Z2yov5jWbAjFIa647KF50ipVfL6ohiTubtwQ1YC9FkevzfCFK3zZwplA/3suLtrxNldEqguAW7usacEOH7it+9A== 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: List-Subscribe: List-Unsubscribe: On Tue, Jun 04, 2024 at 05:24:46PM -0700, Andrii Nakryiko wrote: > +/* > + * find_and_lock_vma_rcu() - Find and lock the VMA for a given address, or the > + * next VMA. Search is done under RCU protection, without taking or assuming > + * mmap_lock. Returned VMA is guaranteed to be stable and not isolated. You know this is supposed to be the _short_ description, right? Three lines is way too long. The full description goes between the arguments and the Return: line. > + * @mm: The mm_struct to check > + * @addr: The address > + * > + * Returns: The VMA associated with addr, or the next VMA. > + * May return %NULL in the case of no VMA at addr or above. > + * If the VMA is being modified and can't be locked, -EBUSY is returned. > + */ > +struct vm_area_struct *find_and_lock_vma_rcu(struct mm_struct *mm, > + unsigned long address) > +{ > + MA_STATE(mas, &mm->mm_mt, address, address); > + struct vm_area_struct *vma; > + int err; > + > + rcu_read_lock(); > +retry: > + vma = mas_find(&mas, ULONG_MAX); > + if (!vma) { > + err = 0; /* no VMA, return NULL */ > + goto inval; > + } > + > + if (!vma_start_read(vma)) { > + err = -EBUSY; > + goto inval; > + } > + > + /* > + * Check since vm_start/vm_end might change before we lock the VMA. > + * Note, unlike lock_vma_under_rcu() we are searching for VMA covering > + * address or the next one, so we only make sure VMA wasn't updated to > + * end before the address. > + */ > + if (unlikely(vma->vm_end <= address)) { > + err = -EBUSY; > + goto inval_end_read; > + } > + > + /* Check if the VMA got isolated after we found it */ > + if (vma->detached) { > + vma_end_read(vma); > + count_vm_vma_lock_event(VMA_LOCK_MISS); > + /* The area was replaced with another one */ Surely you need to mas_reset() before you goto retry? > + goto retry; > + }