From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 12 Jun 2003 13:49:46 -0700 From: Andrew Morton Subject: Re: [PATCH] Fix vmtruncate race and distributed filesystem race Message-Id: <20030612134946.450e0f77.akpm@digeo.com> In-Reply-To: <133430000.1055448961@baldur.austin.ibm.com> References: <133430000.1055448961@baldur.austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave McCracken Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Dave McCracken wrote: > > > Paul McKenney and I sat down today and hashed out just what the races are > for both vmtruncate and the distributed filesystems. We took Andrea's > idea of using seqlocks and came up with a simple solution that definitely > fixes the race in vmtruncate, as well as most likely the invalidate race in > distributed filesystems. Paul is going to discuss it with the DFS folks to > verify that it's a complete fix for them, but neither of us can see a hole. > > + seqlock_init(&(mtd_rawdevice->as.truncate_lock)); Why cannot this just be an atomic_t? > + /* Protect against page fault */ > + write_seqlock(&mapping->truncate_lock); > + write_sequnlock(&mapping->truncate_lock); See, this just does foo++. > + /* > + * If someone invalidated the page, serialize against the inode, > + * then go try again. > + */ This comment is inaccurate. "If this vma is file-backed and someone has truncated that file, this page may have been invalidated". > + if (unlikely(read_seqretry(&mapping->truncate_lock, sequence))) { > + spin_unlock(&mm->page_table_lock); > + down(&inode->i_sem); > + up(&inode->i_sem); > + goto retry; > + } > + mm/memory.c shouldn't know about inodes (ok, vmtruncate() should be in filemap.c). How about you do this: do_no_page() { int sequence = 0; ... retry: new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, &sequence); .... if (vma->vm_ops->revalidate && vma->vm_opa->revalidate(vma, sequence)) goto retry; } filemap_nopage(..., int *sequence) { ... *sequence = atomic_read(&mapping->truncate_sequence); ... } int filemap_revalidate(vma, sequence) { struct address_space *mapping; mapping = vma->vm_file->f_dentry->d_inode->i_mapping; return sequence - atomic_read(&mapping->truncate_sequence); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org