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[49.181.47.239]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-710e58735f9sm267932b3a.2.2024.08.09.16.05.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Aug 2024 16:05:43 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1scYg0-00BQM9-1s; Sat, 10 Aug 2024 09:05:40 +1000 Date: Sat, 10 Aug 2024 09:05:40 +1000 From: Dave Chinner To: Josef Bacik Cc: kernel-team@fb.com, linux-fsdevel@vger.kernel.org, jack@suse.cz, amir73il@gmail.com, brauner@kernel.org, linux-xfs@vger.kernel.org, gfs2@lists.linux.dev, linux-bcachefs@vger.kernel.org Subject: Re: [PATCH v3 13/16] fsnotify: generate pre-content permission event on page fault Message-ID: References: <192b90df727e968ca3a17b6b128c10f3575bf6a3.1723228772.git.josef@toxicpanda.com> Precedence: bulk X-Mailing-List: linux-bcachefs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <192b90df727e968ca3a17b6b128c10f3575bf6a3.1723228772.git.josef@toxicpanda.com> On Fri, Aug 09, 2024 at 02:44:21PM -0400, Josef Bacik wrote: > FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending > on the faulting method. > > This pre-content event is meant to be used by hierarchical storage > managers that want to fill in the file content on first read access. > > Export a simple helper that file systems that have their own ->fault() > will use, and have a more complicated helper to be do fancy things with > in filemap_fault. > > Signed-off-by: Josef Bacik .... > +/** > + * filemap_maybe_emit_fsnotify_event - maybe emit a pre-content event. > + * @vmf: struct vm_fault containing details of the fault. > + * > + * If we have a pre-content watch on this file we will emit an event for this > + * range. If we return anything the fault caller should return immediately, we > + * will return VM_FAULT_RETRY if we had to emit an event, which will trigger the > + * fault again and then the fault handler will run the second time through. > + * > + * Return: a bitwise-OR of %VM_FAULT_ codes, 0 if nothing happened. > + */ > +vm_fault_t filemap_maybe_emit_fsnotify_event(struct vm_fault *vmf) > +{ > + struct file *fpin = NULL; > + vm_fault_t ret; > + > + ret = __filemap_maybe_emit_fsnotify_event(vmf, &fpin); > + if (ret) { > + if (fpin) > + fput(fpin); > + return ret; > + } else if (fpin) { > + fput(fpin); > + return VM_FAULT_RETRY; > + } Logic is back to front. Both paths have to check for fpin, only one fpin path needs to modify ret: ret = __filemap_maybe_emit_fsnotify_event(vmf, &fpin); if (fpin) { fput(fpin); if (!ret) ret = VM_FAULT_RETRY; } return ret; > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(filemap_maybe_emit_fsnotify_event); > + > /** > * filemap_fault - read in file data for page fault handling > * @vmf: struct vm_fault containing details of the fault > @@ -3299,6 +3391,19 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > if (unlikely(index >= max_idx)) > return VM_FAULT_SIGBUS; > > + /* > + * If we have pre-content watchers then we need to generate events on > + * page fault so that we can populate any data before the fault. > + */ > + ret = __filemap_maybe_emit_fsnotify_event(vmf, &fpin); > + if (unlikely(ret)) { > + if (fpin) { > + fput(fpin); > + ret |= VM_FAULT_RETRY; > + } > + return ret; > + } Why do we or in VM_FAULT_RETRY here where as the previous case we simply return VM_FAULT_RETRY? Which one of these is wrong? If both are correct, then a comment explaining this is in order... -Dave. -- Dave Chinner david@fromorbit.com