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Commit d7065da0 authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 176306f5

fs/aio.c

+3 −3
Original line number Diff line number Diff line
@@ -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);

fs/file_table.c

+10 −11
Original line number Diff line number Diff line
@@ -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;

include/linux/file.h

+0 −1
Original line number Diff line number Diff line
@@ -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);

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -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