[PATCH 11/15] tty: audit: Remove tty_audit_buf reference counting

When tty_audit_exit() is called from do_exit(), the process is single-threaded. Since the tty_audit_buf is only shared by threads of a process, no other thread can be concurrently accessing the tty_audit_buf during or after tty_audit_exit(). Thus, no other thread can be holding an extra tty_audit_buf reference which would prevent tty_audit_exit() from freeing the tty_audit_buf. As that is the only purpose of the ref counting, remove the reference counting and free the tty_audit_buf directly. Cc: Oleg Nesterov <oleg(a)redhat.com&gt; Signed-off-by: Peter Hurley <peter(a)hurleysoftware.com&gt; --- drivers/tty/tty_audit.c | 47 +++++++---------------------------------------- 1 file changed, 7 insertions(+), 40 deletions(-) diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c index 7943984..71ba8ba 100644 --- a/drivers/tty/tty_audit.c +++ b/drivers/tty/tty_audit.c @@ -14,7 +14,6 @@ #include <linux/tty.h> struct tty_audit_buf { - atomic_t count; struct mutex mutex; /* Protects all data below */ dev_t dev; /* The TTY which the data is from */ unsigned icanon:1; @@ -32,7 +31,6 @@ static struct tty_audit_buf *tty_audit_buf_alloc(void) buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL); if (!buf->data) goto err_buf; - atomic_set(&buf->count, 1); mutex_init(&buf->mutex); buf->dev = MKDEV(0, 0); buf->icanon = 0; @@ -52,12 +50,6 @@ static void tty_audit_buf_free(struct tty_audit_buf *buf) kfree(buf); } -static void tty_audit_buf_put(struct tty_audit_buf *buf) -{ - if (atomic_dec_and_test(&buf->count)) - tty_audit_buf_free(buf); -} - static void tty_audit_log(const char *description, dev_t dev, unsigned char *data, size_t size) { @@ -106,6 +98,9 @@ static void tty_audit_buf_push(struct tty_audit_buf *buf) * * Make sure all buffered data is written out and deallocate the buffer. * Only needs to be called if current->signal->tty_audit_buf != %NULL. + * + * The process is single-threaded at this point; no other threads share + * current->signal. */ void tty_audit_exit(void) { @@ -116,11 +111,8 @@ void tty_audit_exit(void) if (!buf) return; - mutex_lock(&buf->mutex); tty_audit_buf_push(buf); - mutex_unlock(&buf->mutex); - - tty_audit_buf_put(buf); + tty_audit_buf_free(buf); } /** @@ -140,21 +132,14 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch) { struct tty_audit_buf *buf; dev_t dev; - unsigned long flags; - - spin_lock_irqsave(&current->sighand->siglock, flags); - buf = current->signal->tty_audit_buf; - if (buf) - atomic_inc(&buf->count); - spin_unlock_irqrestore(&current->sighand->siglock, flags); dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index; + buf = current->signal->tty_audit_buf; if (buf) { mutex_lock(&buf->mutex); if (buf->dev == dev) tty_audit_buf_push(buf); mutex_unlock(&buf->mutex); - tty_audit_buf_put(buf); } if (audit_enabled && (current->signal->audit_tty & AUDIT_TTY_ENABLE)) { @@ -175,23 +160,15 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch) int tty_audit_push(void) { struct tty_audit_buf *buf; - unsigned long flags; if (~current->signal->audit_tty & AUDIT_TTY_ENABLE) return -EPERM; - spin_lock_irqsave(&current->sighand->siglock, flags); buf = current->signal->tty_audit_buf; - if (buf) - atomic_inc(&buf->count); - spin_unlock_irqrestore(&current->sighand->siglock, flags); - if (buf) { mutex_lock(&buf->mutex); tty_audit_buf_push(buf); mutex_unlock(&buf->mutex); - - tty_audit_buf_put(buf); } return 0; } @@ -207,15 +184,9 @@ static struct tty_audit_buf *tty_audit_buf_get(void) struct tty_audit_buf *buf, *buf2; unsigned long flags; - buf = NULL; - buf2 = NULL; - spin_lock_irqsave(&current->sighand->siglock, flags); buf = current->signal->tty_audit_buf; - if (buf) { - atomic_inc(&buf->count); - goto out; - } - spin_unlock_irqrestore(&current->sighand->siglock, flags); + if (buf) + return buf; buf2 = tty_audit_buf_alloc(); if (buf2 == NULL) { @@ -230,9 +201,6 @@ static struct tty_audit_buf *tty_audit_buf_get(void) buf = buf2; buf2 = NULL; } - atomic_inc(&buf->count); - /* Fall through */ - out: spin_unlock_irqrestore(&current->sighand->siglock, flags); if (buf2) tty_audit_buf_free(buf2); @@ -289,5 +257,4 @@ void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size) tty_audit_buf_push(buf); } while (size != 0); mutex_unlock(&buf->mutex); - tty_audit_buf_put(buf); } -- 2.6.3