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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=UmCv77ojMXG+c1Fp7DLXkEEMvKlYSuA0abYrccWopi8=; b=Cw8dx8w3mnRQxhUnMSVe9PeY6hGAbw183XL2zSYVtmIcHemI/7g0b/EzozGiGqD/D2 ra0blAHvHEgquyEGeYDiOMIM7QsQm2JyAak8vQA98CO2mbthO8kpTe9XgkBdiEc4STdA mnJRA5PedVgHmTxFX79TzjMa0CplQyvh5LFuUrKeJe2UDa7gvKSOSgJ4jqnDCSeMiEvt dJow0AlkyiPuuhuhsbVYDZE/6X5cgLj9YsDrVoymvbqyTcMd7/yjRC52G9oIHOJ7Wocb TRBUaskiY8nuGgAYZ4g0qjIggvqyZDIKDuUEe9kRM8bzNQrWcM1yxAqMzUwOOOw2sMUB kT+w== X-Gm-Message-State: APjAAAWASpH3L547oVcteE2EtwAsnY5UXj+xlMmqtcdlioA1oGVzxF+8 1puKdac9Lq91Iq5uP96BCbAE7nwN8vqcE6/phq6raw== X-Google-Smtp-Source: APXvYqzFh/C6cDrkSdzIHZQLhSVRwEaU4gGSzclCCpHMgWTGugVQoxN/zVlngGYGKq3CVngNXUCDkIhtZyPn6qxtEko= X-Received: by 2002:a9d:7f8b:: with SMTP id t11mr72319otp.110.1558621960440; Thu, 23 May 2019 07:32:40 -0700 (PDT) MIME-Version: 1.0 References: <20190522155259.11174-1-christian@brauner.io> <20190522165737.GC4915@redhat.com> <20190523115118.pmscbd6kaqy37dym@brauner.io> In-Reply-To: <20190523115118.pmscbd6kaqy37dym@brauner.io> From: Jann Horn Date: Thu, 23 May 2019 16:32:14 +0200 Message-ID: Subject: Re: [PATCH v1 1/2] open: add close_range() To: Christian Brauner X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190523_073244_600034_BCE49191 X-CRM114-Status: GOOD ( 13.44 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, kernel list , David Howells , "open list:KERNEL SELFTEST FRAMEWORK" , sparclinux@vger.kernel.org, Shuah Khan , linux-arch , linux-s390 , Miklos Szeredi , the arch/x86 maintainers , Linus Torvalds , linux-xtensa@linux-xtensa.org, Todd Kjos , Arnd Bergmann , linux-m68k@lists.linux-m68k.org, Al Viro , Oleg Nesterov , Thomas Gleixner , "Dmitry V. Levin" , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-parisc@vger.kernel.org, Linux API , linux-mips@vger.kernel.org, linux-alpha@vger.kernel.org, linux-fsdevel , linuxppc-dev@lists.ozlabs.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, May 23, 2019 at 1:51 PM Christian Brauner wrote: [...] > I kept it dumb and was about to reply that your solution introduces more > code when it seemed we wanted to keep this very simple for now. > But then I saw that find_next_opened_fd() already exists as > find_next_fd(). So it's actually not bad compared to what I sent in v1. > So - with some small tweaks (need to test it and all now) - how do we > feel about?: [...] > static int __close_next_open_fd(struct files_struct *files, unsigned *curfd, unsigned maxfd) > { > struct file *file = NULL; > unsigned fd; > struct fdtable *fdt; > > spin_lock(&files->file_lock); > fdt = files_fdtable(files); > fd = find_next_fd(fdt, *curfd); find_next_fd() finds free fds, not used ones. > if (fd >= fdt->max_fds || fd > maxfd) > goto out_unlock; > > file = fdt->fd[fd]; > rcu_assign_pointer(fdt->fd[fd], NULL); > __put_unused_fd(files, fd); You can't do __put_unused_fd() if the old pointer in fdt->fd[fd] was NULL - because that means that the fd has been reserved by another thread that is about to put a file pointer in there, and if you release the fd here, that messes up the refcounting (or hits the BUG_ON() in __fd_install()). > out_unlock: > spin_unlock(&files->file_lock); > > if (!file) > return -EBADF; > > *curfd = fd; > filp_close(file, files); > return 0; > } > > int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd) > { > if (fd > max_fd) > return -EINVAL; > > while (fd <= max_fd) { Note that with a pattern like this, you have to be careful about what happens if someone gives you max_fd==0xffffffff - then this condition is always true and the loop can not terminate this way. > if (__close_next_fd(files, &fd, maxfd)) > break; (obviously it can still terminate this way) > cond_resched(); > fd++; > } > > return 0; > } _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel