Messages in this thread Patch in this message | | | Date | Wed, 25 Apr 2007 21:46:33 +0200 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH] use mutex instead of semaphore in tty_io.c |
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El Wed, Apr 25, 2007 at 08:13:59PM +0100 Christoph Hellwig ha dit:
> On Wed, Apr 25, 2007 at 05:49:34PM +0200, Matthias Kaehlcke wrote: > > drivers/char/tty_io.c uses a semaphore as mutex. use the mutex API > > instead of the (binary) semaphore > > This looks like it should be a spinlock: > > > - down(&allocated_ptys_lock); > > + mutex_lock(&allocated_ptys_lock); > > idr_remove(&allocated_ptys, idx); > > - up(&allocated_ptys_lock); > > + mutex_unlock(&allocated_ptys_lock); > > idr_remove is a quick operation that doesn't sleep. > > > @@ -2639,24 +2639,24 @@ static int ptmx_open(struct inode * inode, struct file * filp) > > nonseekable_open(inode, filp); > > > > /* find a device that is not in use. */ > > - down(&allocated_ptys_lock); > > + mutex_lock(&allocated_ptys_lock); > > if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) { > > - up(&allocated_ptys_lock); > > The idr_pre_get should be moved out of the lock, that's the whole > point for it's existance.. > > > + mutex_unlock(&allocated_ptys_lock); > > return -ENOMEM; > > } > > idr_ret = idr_get_new(&allocated_ptys, NULL, &index); > > if (idr_ret < 0) { > > - up(&allocated_ptys_lock); > > + mutex_unlock(&allocated_ptys_lock); > > if (idr_ret == -EAGAIN) > > return -ENOMEM; > > return -EIO; > > } > > if (index >= pty_limit) { > > idr_remove(&allocated_ptys, index); > > - up(&allocated_ptys_lock); > > + mutex_unlock(&allocated_ptys_lock); > > return -EIO; > > } > > - up(&allocated_ptys_lock); > > + mutex_unlock(&allocated_ptys_lock); > > And idr_get_new is another quick, non-blocking operation.
thanks for your remarks. is the following patch what you are proposing?
-- diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index 7a32df5..ff27587 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -137,7 +137,7 @@ EXPORT_SYMBOL(tty_mutex); extern struct tty_driver *ptm_driver; /* Unix98 pty masters; for /dev/ptmx */ extern int pty_limit; /* Config limit on Unix98 ptys */ static DEFINE_IDR(allocated_ptys); -static DECLARE_MUTEX(allocated_ptys_lock); +static DEFINE_SPINLOCK(allocated_ptys_lock); static int ptmx_open(struct inode *, struct file *); #endif @@ -2471,9 +2471,9 @@ static void release_dev(struct file * filp) #ifdef CONFIG_UNIX98_PTYS /* Make this pty number available for reallocation */ if (devpts) { - down(&allocated_ptys_lock); + spin_lock(&allocated_ptys_lock); idr_remove(&allocated_ptys, idx); - up(&allocated_ptys_lock); + spin_unlock(&allocated_ptys_lock); } #endif @@ -2639,24 +2639,24 @@ static int ptmx_open(struct inode * inode, struct file * filp) nonseekable_open(inode, filp); /* find a device that is not in use. */ - down(&allocated_ptys_lock); - if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) { - up(&allocated_ptys_lock); + if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) return -ENOMEM; - } + + spin_lock(&allocated_ptys_lock); + idr_ret = idr_get_new(&allocated_ptys, NULL, &index); if (idr_ret < 0) { - up(&allocated_ptys_lock); + spin_unlock(&allocated_ptys_lock); if (idr_ret == -EAGAIN) return -ENOMEM; return -EIO; } if (index >= pty_limit) { idr_remove(&allocated_ptys, index); - up(&allocated_ptys_lock); + spin_unlock(&allocated_ptys_lock); return -EIO; } - up(&allocated_ptys_lock); + spin_unlock(&allocated_ptys_lock); mutex_lock(&tty_mutex); retval = init_dev(ptm_driver, index, &tty); @@ -2681,9 +2681,9 @@ out1: release_dev(filp); return retval; out: - down(&allocated_ptys_lock); + spin_lock(&allocated_ptys_lock); idr_remove(&allocated_ptys, index); - up(&allocated_ptys_lock); + spin_unlock(&allocated_ptys_lock); return retval; } #endif -- Matthias Kaehlcke Linux Application Developer Barcelona
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