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Biederman) To: Alexey Gladkov References: <116c7669744404364651e3b380db2d82bb23f983.1610722473.git.gladkov.alexey@gmail.com> <20210118194551.h2hrwof7b3q5vgoi@example.org> <20210118205629.zro2qkd3ut42bpyq@example.org> Date: Tue, 19 Jan 2021 19:57:36 -0600 In-Reply-To: <20210118205629.zro2qkd3ut42bpyq@example.org> (Alexey Gladkov's message of "Mon, 18 Jan 2021 21:56:29 +0100") Message-ID: <87eeig74kv.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1l22li-00B0cw-Bf; ; ; mid=<87eeig74kv.fsf@x220.int.ebiederm.org>; ; ; hst=in02.mta.xmission.com; ; ; ip=68.227.160.95; ; ; frm=ebiederm@xmission.com; ; ; spf=neutral X-XM-AID: U2FsdGVkX1/ggaLsmakqXtb9Zqya1vF2O+oxa+qmtw0= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [RFC PATCH v3 1/8] Use refcount_t for ucounts reference counting X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Cc: Jens Axboe , Kees Cook , Kernel Hardening , Linux Containers , Jann Horn , LKML , Oleg Nesterov , Linux-MM , Andrew Morton , Linus Torvalds , io-uring X-BeenThere: containers@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux Containers List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: containers-bounces@lists.linux-foundation.org Sender: "Containers" Alexey Gladkov writes: > On Mon, Jan 18, 2021 at 12:34:29PM -0800, Linus Torvalds wrote: >> On Mon, Jan 18, 2021 at 11:46 AM Alexey Gladkov >> wrote: >> > >> > Sorry about that. I thought that this code is not needed when switching >> > from int to refcount_t. I was wrong. >> >> Well, you _may_ be right. I personally didn't check how the return >> value is used. >> >> I only reacted to "it certainly _may_ be used, and there is absolutely >> no comment anywhere about why it wouldn't matter". > > I have not found examples where checked the overflow after calling > refcount_inc/refcount_add. > > For example in kernel/fork.c:2298 : > > current->signal->nr_threads++; > atomic_inc(¤t->signal->live); > refcount_inc(¤t->signal->sigcnt); > > $ semind search signal_struct.sigcnt > def include/linux/sched/signal.h:83 refcount_t sigcnt; > m-- kernel/fork.c:723 put_signal_struct if (refcount_dec_and_test(&sig->sigcnt)) > m-- kernel/fork.c:1571 copy_signal refcount_set(&sig->sigcnt, 1); > m-- kernel/fork.c:2298 copy_process refcount_inc(¤t->signal->sigcnt); > > It seems to me that the only way is to use __refcount_inc and then compare > the old value with REFCOUNT_MAX > > Since I have not seen examples of such checks, I thought that this is > acceptable. Sorry once again. I have not tried to hide these changes. The current ucount code does check for overflow and fails the increment in every case. So arguably it will be a regression and inferior error handling behavior if the code switches to the ``better'' refcount_t data structure. I originally didn't use refcount_t because silently saturating and not bothering to handle the error makes me uncomfortable. Not having to acquire the ucounts_lock every time seems nice. Perhaps the path forward would be to start with stupid/correct code that always takes the ucounts_lock for every increment of ucounts->count, that is later replaced with something more optimal. Not impacting performance in the non-namespace cases and having good performance in the other cases is a fundamental requirement of merging code like this. Eric _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/containers