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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-09-18 22:59:29 +02:00
Takashi Iwai
7ffa5d2462
Each virmidi device keeps a list of its opened input files (filelist) protected by both an rwlock (filelist_lock) and a rw_semaphore (filelist_sem). snd_virmidi_dev_receive_event() walks the list on the sequencer event input path -- read_lock() when the event is delivered in atomic context, down_read() otherwise -- decoding each incoming event into the file's rawmidi buffer. The writers (input open/close) take both locks to add/remove entries. This is another typical dual-lock read-mostly pattern as the port subscriber list: files are opened/closed rarely while the receive callback runs per event. Let's convert the traversal to RCU and drop the rwlock; the existing filelist_sem keeps serializing the writers. The atomic input path now runs lock-free under rcu_read_lock(), and both readers share a single list_for_each_entry_rcu() (valid under the rwsem via lockdep_is_held()). The writers switch to list_add_tail_rcu() / list_del_rcu(). snd_virmidi_input_close() freed the entry (parser and struct) immediately after list_del. A concurrent lockless reader in the atomic path may still be dereferencing it, so the close path now waits for an RCU grace period after list_del_rcu() before freeing; synchronize_rcu() is used rather than kfree_rcu() because the parser must also be released after the grace period, not just the struct. Non-atomic readers are already excluded by the down_write, so only the atomic RCU readers need the grace period. Dropping write_lock_irq() from the writers is safe: no writer runs in atomic/IRQ context, and the sole atomic reader now uses RCU, which is IRQ-safe. Signed-off-by: Takashi Iwai <tiwai@suse.de> Link: https://patch.msgid.link/20260810133711.42483-5-tiwai@suse.de
69 lines
2.0 KiB
C
69 lines
2.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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#ifndef __SOUND_SEQ_VIRMIDI_H
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#define __SOUND_SEQ_VIRMIDI_H
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/*
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* Virtual Raw MIDI client on Sequencer
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* Copyright (c) 2000 by Takashi Iwai <tiwai@suse.de>,
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* Jaroslav Kysela <perex@perex.cz>
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*/
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#include <sound/rawmidi.h>
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#include <sound/seq_midi_event.h>
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/*
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* device file instance:
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* This instance is created at each time the midi device file is
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* opened. Each instance has its own input buffer and MIDI parser
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* (buffer), and is associated with the device instance.
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*/
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struct snd_virmidi {
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struct list_head list;
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int seq_mode;
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int client;
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int port;
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bool trigger;
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struct snd_midi_event *parser;
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struct snd_seq_event event;
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struct snd_virmidi_dev *rdev;
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struct snd_rawmidi_substream *substream;
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struct work_struct output_work;
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};
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#define SNDRV_VIRMIDI_SUBSCRIBE (1<<0)
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#define SNDRV_VIRMIDI_USE (1<<1)
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/*
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* device record:
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* Each virtual midi device has one device instance. It contains
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* common information and the linked-list of opened files,
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*/
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struct snd_virmidi_dev {
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struct snd_card *card; /* associated card */
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struct snd_rawmidi *rmidi; /* rawmidi device */
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int seq_mode; /* SNDRV_VIRMIDI_XXX */
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int device; /* sequencer device */
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int client; /* created/attached client */
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int port; /* created/attached port */
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unsigned int flags; /* SNDRV_VIRMIDI_* */
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struct rw_semaphore filelist_sem;
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struct list_head filelist;
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};
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/* sequencer mode:
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* ATTACH = input/output events from midi device are routed to the
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* attached sequencer port. sequencer port is not created
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* by virmidi itself.
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* the input to rawmidi must be processed by passing the
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* incoming events via snd_virmidi_receive()
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* DISPATCH = input/output events are routed to subscribers.
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* sequencer port is created in virmidi.
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*/
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#define SNDRV_VIRMIDI_SEQ_NONE 0
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#define SNDRV_VIRMIDI_SEQ_ATTACH 1
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#define SNDRV_VIRMIDI_SEQ_DISPATCH 2
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int snd_virmidi_new(struct snd_card *card, int device, struct snd_rawmidi **rrmidi);
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#endif /* __SOUND_SEQ_VIRMIDI */
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