Messages in this thread Patch in this message | | | Date | Mon, 30 Mar 2009 08:01:50 -0600 | From | Jonathan Corbet <> | Subject | Re: WARNING: at net/ipv4/tcp_input.c:2927 tcp_ack+0xd55/0x1991() |
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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.
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
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