From db1dd4d376134eba0e08af523b61cc566a4ea1cd Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Fri, 6 Feb 2009 15:25:24 -0700 Subject: Use f_lock to protect f_flags Traditionally, changes to struct file->f_flags have been done under BKL protection, or with no protection at all. This patch causes all f_flags changes after file open/creation time to be done under protection of f_lock. This allows the removal of some BKL usage and fixes a number of longstanding (if microscopic) races. Reviewed-by: Christoph Hellwig Cc: Al Viro Signed-off-by: Jonathan Corbet --- fs/fcntl.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/fcntl.c') diff --git a/fs/fcntl.c b/fs/fcntl.c index bd215cc791da..04df8570a2d2 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -189,7 +189,9 @@ static int setfl(int fd, struct file * filp, unsigned long arg) } } + spin_lock(&filp->f_lock); filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK); + spin_unlock(&filp->f_lock); out: unlock_kernel(); return error; -- cgit v1.2.2 From 76398425bb06b07cc3a3b1ce169c67dc9d6874ed Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Sun, 1 Feb 2009 14:26:59 -0700 Subject: 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 Cc: David Miller Reviewed-by: Christoph Hellwig Signed-off-by: Jonathan Corbet --- fs/fcntl.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) (limited to 'fs/fcntl.c') diff --git a/fs/fcntl.c b/fs/fcntl.c index 04df8570a2d2..431bb6459273 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -141,7 +141,7 @@ SYSCALL_DEFINE1(dup, unsigned int, fildes) return ret; } -#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | FASYNC | O_DIRECT | O_NOATIME) +#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME) static int setfl(int fd, struct file * filp, unsigned long arg) { @@ -177,23 +177,19 @@ static int setfl(int fd, struct file * filp, unsigned long arg) return error; /* - * We still need a lock here for now to keep multiple FASYNC calls - * from racing with each other. + * ->fasync() is responsible for setting the FASYNC bit. */ - lock_kernel(); - if ((arg ^ filp->f_flags) & FASYNC) { - if (filp->f_op && filp->f_op->fasync) { - error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0); - if (error < 0) - goto out; - } + if (((arg ^ filp->f_flags) & FASYNC) && filp->f_op && + filp->f_op->fasync) { + error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0); + if (error < 0) + goto out; } - spin_lock(&filp->f_lock); filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK); spin_unlock(&filp->f_lock); + out: - unlock_kernel(); return error; } @@ -518,7 +514,7 @@ static DEFINE_RWLOCK(fasync_lock); static struct kmem_cache *fasync_cache __read_mostly; /* - * fasync_helper() is used by some character device drivers (mainly mice) + * fasync_helper() is used by almost all character device drivers * to set up the fasync queue. It returns negative on error, 0 if it did * no changes and positive if it added/deleted the entry. */ @@ -557,6 +553,13 @@ 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); return result; } -- cgit v1.2.2 From 60aa49243d09afc873f082567d2e3c16634ced84 Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Sun, 1 Feb 2009 14:52:56 -0700 Subject: Rationalize fasync return values Most fasync implementations do something like: return fasync_helper(...); But fasync_helper() will return a positive value at times - a feature used in at least one place. Thus, a number of other drivers do: err = fasync_helper(...); if (err < 0) return err; return 0; In the interests of consistency and more concise code, it makes sense to map positive return values onto zero where ->fasync() is called. Cc: Al Viro Signed-off-by: Jonathan Corbet --- fs/fcntl.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/fcntl.c') diff --git a/fs/fcntl.c b/fs/fcntl.c index 431bb6459273..d865ca66ccba 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -184,6 +184,8 @@ static int setfl(int fd, struct file * filp, unsigned long arg) error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0); if (error < 0) goto out; + if (error > 0) + error = 0; } spin_lock(&filp->f_lock); filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK); -- cgit v1.2.2 From 4a6a4499693a419a20559c41e33a7bd70bf20a6f Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Fri, 27 Mar 2009 12:24:31 -0600 Subject: 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 Reported-by: Larry Finger Reported-by: Wu Fengguang Signed-off-by: Jonathan Corbet --- fs/fcntl.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'fs/fcntl.c') diff --git a/fs/fcntl.c b/fs/fcntl.c index d865ca66ccba..cc8e4de2fee5 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; } -- cgit v1.2.2