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Commit c02b1a9b authored by Mateusz Guzik's avatar Mateusz Guzik Committed by Al Viro
Browse files

vfs: grab the lock instead of blocking in __fd_install during resizing 



Explicit locking in the fallback case provides a safe state of the
table. Getting rid of blocking semantics makes __fd_install usable
again in non-sleepable contexts, which easies backporting efforts.

There is a side effect of slightly nicer assembly for the common case
as might_sleep can now be removed.

Signed-off-by: default avatarMateusz Guzik <mguzik@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 52979082

Documentation/filesystems/porting

+0 −4
Original line number Diff line number Diff line
@@ -501,10 +501,6 @@ in your dentry operations instead. 
	is non-NULL.  Note that link body isn't available anymore, so if you need it,

	store it as cookie.

--

[mandatory]

	__fd_install() & fd_install() can now sleep. Callers should not

	hold a spinlock	or other resources that do not allow a schedule.

--

[mandatory]

	any symlink that might use page_follow_link_light/page_put_link() must

	have inode_nohighmem(inode) called before anything might start playing with

fs/file.c

+7 −4
Original line number Diff line number Diff line
@@ -592,13 +592,16 @@ void __fd_install(struct files_struct *files, unsigned int fd, 
{

	struct fdtable *fdt;



	might_sleep();

	rcu_read_lock_sched();



	while (unlikely(files->resize_in_progress)) {

	if (unlikely(files->resize_in_progress)) {

		rcu_read_unlock_sched();

		wait_event(files->resize_wait, !files->resize_in_progress);

		rcu_read_lock_sched();

		spin_lock(&files->file_lock);

		fdt = files_fdtable(files);

		BUG_ON(fdt->fd[fd] != NULL);

		rcu_assign_pointer(fdt->fd[fd], file);

		spin_unlock(&files->file_lock);

		return;

	}

	/* coupled with smp_wmb() in expand_fdtable() */

	smp_rmb();