| Message ID | 20090330080150.724378b0@bike.lwn.net |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On Mon, Mar 30, 2009 at 08:01:50AM -0600, Jonathan Corbet wrote: > On Mon, 30 Mar 2009 08:51:07 +0000 > Jarek Poplawski <jarkao2@gmail.com> wrote: > > > Probably I miss something, but generally in a case like this "a_lock" > > doesn't have to be taken in IRQ mode to be dangerous. Eg. if one cpu > > is trying to take this lock after fasync_lock (with IRQs disabled), > > while another cpu is waiting for fasync_lock in IRQ, which preempted > > such "a_lock". > > The possibility exists, I guess, yes. > > > Could you give some details of this fix? > > I just reverse the order of lock acquisition in fasync_helper(). Patch > is attached. I'll be sending up a pull request shortly. Yes, this patch should fix this. (And I can see it in the linux-next now...) Thanks, Jarek P. > > jon > > From 4a6a4499693a419a20559c41e33a7bd70bf20a6f Mon Sep 17 00:00:00 2001 > From: Jonathan Corbet <corbet@lwn.net> > Date: Fri, 27 Mar 2009 12:24:31 -0600 > Subject: [PATCH] Fix a lockdep warning in fasync_helper() > > Lockdep gripes if file->f_lock is taken in a no-IRQ situation, since that > is not always the case. We don't really want to disable IRQs for every > acquisition of f_lock; instead, just move it outside of fasync_lock. > > Reported-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> > Reported-by: Larry Finger <Larry.Finger@lwfinger.net> > Reported-by: Wu Fengguang <fengguang.wu@intel.com> > Signed-off-by: Jonathan Corbet <corbet@lwn.net> > --- > fs/fcntl.c | 10 +++++++--- > include/linux/fs.h | 2 +- > 2 files changed, 8 insertions(+), 4 deletions(-) > > diff --git a/fs/fcntl.c b/fs/fcntl.c > index d865ca6..cc8e4de 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -531,6 +531,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap > if (!new) > return -ENOMEM; > } > + > + /* > + * We need to take f_lock first since it's not an IRQ-safe > + * lock. > + */ > + spin_lock(&filp->f_lock); > write_lock_irq(&fasync_lock); > for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) { > if (fa->fa_file == filp) { > @@ -555,14 +561,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap > result = 1; > } > out: > - /* Fix up FASYNC bit while still holding fasync_lock */ > - spin_lock(&filp->f_lock); > if (on) > filp->f_flags |= FASYNC; > else > filp->f_flags &= ~FASYNC; > - spin_unlock(&filp->f_lock); > write_unlock_irq(&fasync_lock); > + spin_unlock(&filp->f_lock); > return result; > } > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 7428c6d..2f13c1d 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -848,7 +848,7 @@ struct file { > #define f_dentry f_path.dentry > #define f_vfsmnt f_path.mnt > const struct file_operations *f_op; > - spinlock_t f_lock; /* f_ep_links, f_flags */ > + spinlock_t f_lock; /* f_ep_links, f_flags, no IRQ */ > atomic_long_t f_count; > unsigned int f_flags; > fmode_t f_mode; > -- > 1.6.2 > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/fcntl.c b/fs/fcntl.c index d865ca6..cc8e4de 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -531,6 +531,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap if (!new) return -ENOMEM; } + + /* + * We need to take f_lock first since it's not an IRQ-safe + * lock. + */ + spin_lock(&filp->f_lock); write_lock_irq(&fasync_lock); for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) { if (fa->fa_file == filp) { @@ -555,14 +561,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap result = 1; } out: - /* Fix up FASYNC bit while still holding fasync_lock */ - spin_lock(&filp->f_lock); if (on) filp->f_flags |= FASYNC; else filp->f_flags &= ~FASYNC; - spin_unlock(&filp->f_lock); write_unlock_irq(&fasync_lock); + spin_unlock(&filp->f_lock); return result; } diff --git a/include/linux/fs.h b/include/linux/fs.h index 7428c6d..2f13c1d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -848,7 +848,7 @@ struct file { #define f_dentry f_path.dentry #define f_vfsmnt f_path.mnt const struct file_operations *f_op; - spinlock_t f_lock; /* f_ep_links, f_flags */ + spinlock_t f_lock; /* f_ep_links, f_flags, no IRQ */ atomic_long_t f_count; unsigned int f_flags; fmode_t f_mode;