Commit c1221321 authored Jul 07, 2014 by NeilBrown Committed by Ingo Molnar Jul 16, 2014

sched: Allow wait_on_bit_action() functions to support a timeout



It is currently not possible for various wait_on_bit functions
to implement a timeout.

While the "action" function that is called to do the waiting
could certainly use schedule_timeout(), there is no way to carry
forward the remaining timeout after a false wake-up.
As false-wakeups a clearly possible at least due to possible
hash collisions in bit_waitqueue(), this is a real problem.

The 'action' function is currently passed a pointer to the word
containing the bit being waited on.  No current action functions
use this pointer.  So changing it to something else will be a
little noisy but will have no immediate effect.

This patch changes the 'action' function to take a pointer to
the "struct wait_bit_key", which contains a pointer to the word
containing the bit so nothing is really lost.

It also adds a 'private' field to "struct wait_bit_key", which
is initialized to zero.

An action function can now implement a timeout with something
like

static int timed_out_waiter(struct wait_bit_key *key)
{
	unsigned long waited;
	if (key->private == 0) {
		key->private = jiffies;
		if (key->private == 0)
			key->private -= 1;
	}
	waited = jiffies - key->private;
	if (waited > 10 * HZ)
		return -EAGAIN;
	schedule_timeout(waited - 10 * HZ);
	return 0;
}

If any other need for context in a waiter were found it would be
easy to use ->private for some other purpose, or even extend
"struct wait_bit_key".

My particular need is to support timeouts in nfs_release_page()
to avoid deadlocks with loopback mounted NFS.

While wait_on_bit_timeout() would be a cleaner interface, it
will not meet my need.  I need the timeout to be sensitive to
the state of the connection with the server, which could change.
 So I need to use an 'action' interface.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steve French <sfrench@samba.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140707051604.28027.41257.stgit@notabene.brown


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 74316201

fs/cifs/inode.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1780,7 +1780,7 @@ cifs_invalidate_mapping(struct inode *inode)
		* @word: long word containing the bit lock
		*/
		static int
		cifs_wait_bit_killable(void *word)
		cifs_wait_bit_killable(struct wait_bit_key *key)
		{
		if (fatal_signal_pending(current))
		return -ERESTARTSYS;

fs/nfs/inode.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -75,7 +75,7 @@ nfs_fattr_to_ino_t(struct nfs_fattr *fattr)
		* nfs_wait_bit_killable - helper for functions that are sleeping on bit locks
		* @word: long word containing the bit lock
		*/
		int nfs_wait_bit_killable(void *word)
		int nfs_wait_bit_killable(struct wait_bit_key *key)
		{
		if (fatal_signal_pending(current))
		return -ERESTARTSYS;

fs/nfs/internal.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -347,7 +347,7 @@ extern int nfs_drop_inode(struct inode *);
		extern void nfs_clear_inode(struct inode *);
		extern void nfs_evict_inode(struct inode *);
		void nfs_zap_acl_cache(struct inode *inode);
		extern int nfs_wait_bit_killable(void *word);
		extern int nfs_wait_bit_killable(struct wait_bit_key *key);

		/* super.c */
		extern const struct super_operations nfs_sops;

fs/nfs/pagelist.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -117,7 +117,7 @@ __nfs_iocounter_wait(struct nfs_io_counter *c)
		set_bit(NFS_IO_INPROGRESS, &c->flags);
		if (atomic_read(&c->io_count) == 0)
		break;
		ret = nfs_wait_bit_killable(&c->flags);
		ret = nfs_wait_bit_killable(&q.key);
		} while (atomic_read(&c->io_count) != 0);
		finish_wait(wq, &q.wait);
		return ret;

include/linux/sunrpc/sched.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -236,7 +236,7 @@ void * rpc_malloc(struct rpc_task *, size_t);
		void rpc_free(void *);
		int rpciod_up(void);
		void rpciod_down(void);
		int __rpc_wait_for_completion_task(struct rpc_task task, int ()(void *));
		int __rpc_wait_for_completion_task(struct rpc_task task, wait_bit_action_f );
		#ifdef RPC_DEBUG
		struct net;
		void rpc_show_tasks(struct net *);

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