From d7065da038227a4d09a244e6014e0186a6bd21d0 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 26 May 2010 15:13:55 -0400 Subject: [PATCH] get rid of the magic around f_count in aio __aio_put_req() plays sick games with file refcount. What it wants is fput() from atomic context; it's almost always done with f_count > 1, so they only have to deal with delayed work in rare cases when their reference happens to be the last one. Current code decrements f_count and if it hasn't hit 0, everything is fine. Otherwise it keeps a pointer to struct file (with zero f_count!) around and has delayed work do __fput() on it. Better way to do it: use atomic_long_add_unless( , -1, 1) instead of !atomic_long_dec_and_test(). IOW, decrement it only if it's not the last reference, leave refcount alone if it was. And use normal fput() in delayed work. I've made that atomic_long_add_unless call a new helper - fput_atomic(). Drops a reference to file if it's safe to do in atomic (i.e. if that's not the last one), tells if it had been able to do that. aio.c converted to it, __fput() use is gone. req->ki_file *always* contributes to refcount now. And __fput() became static. Signed-off-by: Al Viro --- fs/aio.c | 6 +++--- fs/file_table.c | 21 ++++++++++----------- include/linux/file.h | 1 - include/linux/fs.h | 1 + 4 files changed, 14 insertions(+), 15 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index 48fdeebdb544..1ccf25cef1f0 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -527,7 +527,7 @@ static void aio_fput_routine(struct work_struct *data) /* Complete the fput(s) */ if (req->ki_filp != NULL) - __fput(req->ki_filp); + fput(req->ki_filp); /* Link the iocb into the context's free list */ spin_lock_irq(&ctx->ctx_lock); @@ -560,11 +560,11 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req) /* * Try to optimize the aio and eventfd file* puts, by avoiding to - * schedule work in case it is not __fput() time. In normal cases, + * schedule work in case it is not final fput() time. In normal cases, * we would not be holding the last reference to the file*, so * this function will be executed w/out any aio kthread wakeup. */ - if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) { + if (unlikely(!fput_atomic(req->ki_filp))) { get_ioctx(ctx); spin_lock(&fput_lock); list_add(&req->ki_list, &fput_head); diff --git a/fs/file_table.c b/fs/file_table.c index 32d12b78bac8..5c7d10ead4ad 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -194,14 +194,6 @@ struct file *alloc_file(struct path *path, fmode_t mode, } EXPORT_SYMBOL(alloc_file); -void fput(struct file *file) -{ - if (atomic_long_dec_and_test(&file->f_count)) - __fput(file); -} - -EXPORT_SYMBOL(fput); - /** * drop_file_write_access - give up ability to write to a file * @file: the file to which we will stop writing @@ -227,10 +219,9 @@ void drop_file_write_access(struct file *file) } EXPORT_SYMBOL_GPL(drop_file_write_access); -/* __fput is called from task context when aio completion releases the last - * last use of a struct file *. Do not use otherwise. +/* the real guts of fput() - releasing the last reference to file */ -void __fput(struct file *file) +static void __fput(struct file *file) { struct dentry *dentry = file->f_path.dentry; struct vfsmount *mnt = file->f_path.mnt; @@ -268,6 +259,14 @@ void __fput(struct file *file) mntput(mnt); } +void fput(struct file *file) +{ + if (atomic_long_dec_and_test(&file->f_count)) + __fput(file); +} + +EXPORT_SYMBOL(fput); + struct file *fget(unsigned int fd) { struct file *file; diff --git a/include/linux/file.h b/include/linux/file.h index 5555508fd517..b1e12970f617 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -11,7 +11,6 @@ struct file; -extern void __fput(struct file *); extern void fput(struct file *); extern void drop_file_write_access(struct file *file); diff --git a/include/linux/fs.h b/include/linux/fs.h index 85e823adcd4a..3d9ed8302402 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -954,6 +954,7 @@ extern spinlock_t files_lock; #define file_list_unlock() spin_unlock(&files_lock); #define get_file(x) atomic_long_inc(&(x)->f_count) +#define fput_atomic(x) atomic_long_add_unless(&(x)->f_count, -1, 1) #define file_count(x) atomic_long_read(&(x)->f_count) #ifdef CONFIG_DEBUG_WRITECOUNT -- 2.30.2