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authorJonathan Corbet <corbet@lwn.net>2009-02-01 14:26:59 -0700
committerJonathan Corbet <corbet@lwn.net>2009-03-16 08:32:27 -0600
commit76398425bb06b07cc3a3b1ce169c67dc9d6874ed (patch)
treee6e1800edda88b5592617a950daacf2199587a33 /fs/ioctl.c
parentdb1dd4d376134eba0e08af523b61cc566a4ea1cd (diff)
downloadlinux-76398425bb06b07cc3a3b1ce169c67dc9d6874ed.tar.gz
Move FASYNC bit handling to f_op->fasync()
Removing the BKL from FASYNC handling ran into the challenge of keeping the setting of the FASYNC bit in filp->f_flags atomic with regard to calls to the underlying fasync() function. Andi Kleen suggested moving the handling of that bit into fasync(); this patch does exactly that. As a result, we have a couple of internal API changes: fasync() must now manage the FASYNC bit, and it will be called without the BKL held. As it happens, every fasync() implementation in the kernel with one exception calls fasync_helper(). So, if we make fasync_helper() set the FASYNC bit, we can avoid making any changes to the other fasync() functions - as long as those functions, themselves, have proper locking. Most fasync() implementations do nothing but call fasync_helper() - which has its own lock - so they are easily verified as correct. The BKL had already been pushed down into the rest. The networking code has its own version of fasync_helper(), so that code has been augmented with explicit FASYNC bit handling. Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: David Miller <davem@davemloft.net> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'fs/ioctl.c')
-rw-r--r--fs/ioctl.c13
1 files changed, 1 insertions, 12 deletions
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 421aab465da..e8e89edba57 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -427,19 +427,11 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
/* Did FASYNC state change ? */
if ((flag ^ filp->f_flags) & FASYNC) {
if (filp->f_op && filp->f_op->fasync)
+ /* fasync() adjusts filp->f_flags */
error = filp->f_op->fasync(fd, filp, on);
else
error = -ENOTTY;
}
- if (error)
- return error;
-
- spin_lock(&filp->f_lock);
- if (on)
- filp->f_flags |= FASYNC;
- else
- filp->f_flags &= ~FASYNC;
- spin_unlock(&filp->f_lock);
return error;
}
@@ -507,10 +499,7 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd,
break;
case FIOASYNC:
- /* BKL needed to avoid races tweaking f_flags */
- lock_kernel();
error = ioctl_fioasync(fd, filp, argp);
- unlock_kernel();
break;
case FIOQSIZE: