n_tty: Remove echo_lock
Adding data to echo_buf (via add_echo_byte()) is guaranteed to be single-threaded, since all callers are from the n_tty_receive_buf() path. Processing the echo_buf can be called from either the n_tty_receive_buf() path or the n_tty_write() path; however, these callers are already serialized by output_lock. Publish cumulative echo_head changes to echo_commit; process echo_buf from echo_tail to echo_commit; remove echo_lock. On echo_buf overrun, claim output_lock to serialize changes to echo_tail. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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862eeffef1
Коммит
17bd790740
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@ -106,10 +106,10 @@ struct n_tty_data {
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/* consumer-published */
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size_t read_tail;
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/* protected by echo_lock */
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unsigned char *echo_buf;
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size_t echo_head;
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size_t echo_tail;
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size_t echo_commit;
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/* protected by output lock */
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unsigned int column;
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@ -117,7 +117,6 @@ struct n_tty_data {
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struct mutex atomic_read_lock;
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struct mutex output_lock;
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struct mutex echo_lock;
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};
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static inline size_t read_cnt(struct n_tty_data *ldata)
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@ -333,10 +332,7 @@ static void put_tty_queue(unsigned char c, struct n_tty_data *ldata)
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static void reset_buffer_flags(struct n_tty_data *ldata)
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{
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ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
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mutex_lock(&ldata->echo_lock);
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ldata->echo_head = ldata->echo_tail = 0;
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mutex_unlock(&ldata->echo_lock);
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ldata->echo_head = ldata->echo_tail = ldata->echo_commit = 0;
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ldata->erasing = 0;
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bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
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@ -642,8 +638,7 @@ break_out:
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* are prioritized. Also, when control characters are echoed with a
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* prefixed "^", the pair is treated atomically and thus not separated.
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*
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* Locking: output_lock to protect column state and space left,
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* echo_lock to protect the echo buffer
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* Locking: output_lock to protect column state and space left
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*/
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static void process_echoes(struct tty_struct *tty)
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@ -653,16 +648,15 @@ static void process_echoes(struct tty_struct *tty)
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size_t tail;
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unsigned char c;
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if (ldata->echo_head == ldata->echo_tail)
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if (ldata->echo_commit == ldata->echo_tail)
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return;
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mutex_lock(&ldata->output_lock);
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mutex_lock(&ldata->echo_lock);
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space = tty_write_room(tty);
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tail = ldata->echo_tail;
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nr = ldata->echo_head - ldata->echo_tail;
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nr = ldata->echo_commit - ldata->echo_tail;
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while (nr > 0) {
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c = echo_buf(ldata, tail);
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if (c == ECHO_OP_START) {
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@ -779,13 +773,21 @@ static void process_echoes(struct tty_struct *tty)
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ldata->echo_tail = tail;
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mutex_unlock(&ldata->echo_lock);
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mutex_unlock(&ldata->output_lock);
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if (tty->ops->flush_chars)
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tty->ops->flush_chars(tty);
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}
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static void commit_echoes(struct tty_struct *tty)
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{
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struct n_tty_data *ldata = tty->disc_data;
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smp_mb();
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ldata->echo_commit = ldata->echo_head;
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process_echoes(tty);
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}
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/**
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* add_echo_byte - add a byte to the echo buffer
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* @c: unicode byte to echo
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@ -793,13 +795,16 @@ static void process_echoes(struct tty_struct *tty)
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*
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* Add a character or operation byte to the echo buffer.
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*
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* Should be called under the echo lock to protect the echo buffer.
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* Locks: may claim output_lock to prevent concurrent modify of
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* echo_tail by process_echoes().
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*/
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static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
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{
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if (ldata->echo_head - ldata->echo_tail == N_TTY_BUF_SIZE) {
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size_t head = ldata->echo_head;
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mutex_lock(&ldata->output_lock);
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/*
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* Since the buffer start position needs to be advanced,
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* be sure to step by a whole operation byte group.
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@ -811,6 +816,7 @@ static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
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ldata->echo_tail += 2;
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} else
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ldata->echo_tail++;
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mutex_unlock(&ldata->output_lock);
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}
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*echo_buf_addr(ldata, ldata->echo_head++) = c;
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@ -821,16 +827,12 @@ static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
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* @ldata: n_tty data
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*
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* Add an operation to the echo buffer to move back one column.
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*
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* Locking: echo_lock to protect the echo buffer
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*/
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static void echo_move_back_col(struct n_tty_data *ldata)
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{
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mutex_lock(&ldata->echo_lock);
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
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mutex_unlock(&ldata->echo_lock);
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}
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/**
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@ -839,16 +841,12 @@ static void echo_move_back_col(struct n_tty_data *ldata)
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*
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* Add an operation to the echo buffer to set the canon column
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* to the current column.
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*
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* Locking: echo_lock to protect the echo buffer
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*/
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static void echo_set_canon_col(struct n_tty_data *ldata)
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{
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mutex_lock(&ldata->echo_lock);
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
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mutex_unlock(&ldata->echo_lock);
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}
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/**
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@ -864,15 +862,11 @@ static void echo_set_canon_col(struct n_tty_data *ldata)
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* of input. This information will be used later, along with
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* canon column (if applicable), to go back the correct number
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* of columns.
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*
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* Locking: echo_lock to protect the echo buffer
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*/
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static void echo_erase_tab(unsigned int num_chars, int after_tab,
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struct n_tty_data *ldata)
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{
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mutex_lock(&ldata->echo_lock);
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
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@ -884,8 +878,6 @@ static void echo_erase_tab(unsigned int num_chars, int after_tab,
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num_chars |= 0x80;
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add_echo_byte(num_chars, ldata);
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mutex_unlock(&ldata->echo_lock);
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}
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/**
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@ -897,20 +889,16 @@ static void echo_erase_tab(unsigned int num_chars, int after_tab,
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* L_ECHO(tty) is true. Called from the driver receive_buf path.
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*
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* This variant does not treat control characters specially.
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*
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* Locking: echo_lock to protect the echo buffer
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*/
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static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
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{
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mutex_lock(&ldata->echo_lock);
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if (c == ECHO_OP_START) {
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(ECHO_OP_START, ldata);
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} else {
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add_echo_byte(c, ldata);
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}
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mutex_unlock(&ldata->echo_lock);
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}
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/**
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@ -923,16 +911,12 @@ static void echo_char_raw(unsigned char c, struct n_tty_data *ldata)
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*
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* This variant tags control characters to be echoed as "^X"
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* (where X is the letter representing the control char).
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*
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* Locking: echo_lock to protect the echo buffer
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*/
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static void echo_char(unsigned char c, struct tty_struct *tty)
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{
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struct n_tty_data *ldata = tty->disc_data;
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mutex_lock(&ldata->echo_lock);
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if (c == ECHO_OP_START) {
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(ECHO_OP_START, ldata);
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@ -941,8 +925,6 @@ static void echo_char(unsigned char c, struct tty_struct *tty)
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add_echo_byte(ECHO_OP_START, ldata);
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add_echo_byte(c, ldata);
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}
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mutex_unlock(&ldata->echo_lock);
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}
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/**
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@ -1284,7 +1266,7 @@ static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
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if (ldata->canon_head == ldata->read_head)
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echo_set_canon_col(ldata);
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echo_char(c, tty);
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process_echoes(tty);
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commit_echoes(tty);
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}
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if (parmrk)
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put_tty_queue(c, ldata);
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@ -1295,7 +1277,7 @@ static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
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if (I_IXON(tty)) {
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if (c == START_CHAR(tty)) {
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start_tty(tty);
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process_echoes(tty);
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commit_echoes(tty);
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return;
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}
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if (c == STOP_CHAR(tty)) {
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@ -1326,7 +1308,7 @@ send_signal:
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start_tty(tty);
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if (L_ECHO(tty)) {
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echo_char(c, tty);
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process_echoes(tty);
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commit_echoes(tty);
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}
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isig(signal, tty);
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return;
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@ -1345,7 +1327,7 @@ send_signal:
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if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
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(c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
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eraser(c, tty);
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process_echoes(tty);
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commit_echoes(tty);
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return;
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}
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if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
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@ -1355,7 +1337,7 @@ send_signal:
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if (L_ECHOCTL(tty)) {
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echo_char_raw('^', ldata);
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echo_char_raw('\b', ldata);
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process_echoes(tty);
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commit_echoes(tty);
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}
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}
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return;
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@ -1371,7 +1353,7 @@ send_signal:
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echo_char(read_buf(ldata, tail), tty);
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tail++;
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}
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process_echoes(tty);
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commit_echoes(tty);
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return;
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}
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if (c == '\n') {
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@ -1382,7 +1364,7 @@ send_signal:
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}
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if (L_ECHO(tty) || L_ECHONL(tty)) {
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echo_char_raw('\n', ldata);
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process_echoes(tty);
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commit_echoes(tty);
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}
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goto handle_newline;
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}
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@ -1411,7 +1393,7 @@ send_signal:
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if (ldata->canon_head == ldata->read_head)
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echo_set_canon_col(ldata);
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echo_char(c, tty);
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process_echoes(tty);
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commit_echoes(tty);
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}
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/*
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* XXX does PARMRK doubling happen for
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@ -1448,7 +1430,7 @@ handle_newline:
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echo_set_canon_col(ldata);
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echo_char(c, tty);
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}
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process_echoes(tty);
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commit_echoes(tty);
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}
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if (parmrk)
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@ -1713,7 +1695,6 @@ static int n_tty_open(struct tty_struct *tty)
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ldata->overrun_time = jiffies;
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mutex_init(&ldata->atomic_read_lock);
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mutex_init(&ldata->output_lock);
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mutex_init(&ldata->echo_lock);
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/* These are ugly. Currently a malloc failure here can panic */
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ldata->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
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