diff options
author | NeilBrown <neilb@suse.de> | 2014-07-07 01:16:04 -0400 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2014-07-16 09:10:41 -0400 |
commit | c1221321b7c25b53204447cff9949a6d5a7ddddc (patch) | |
tree | b4dc6613ab838dcd71023f5f018306574fc2985a /fs/nfs/pagelist.c | |
parent | 743162013d40ca612b4cb53d3a200dff2d9ab26e (diff) |
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>
Diffstat (limited to 'fs/nfs/pagelist.c')
-rw-r--r-- | fs/nfs/pagelist.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c index 6104d3500b49..745a612dbe22 100644 --- a/fs/nfs/pagelist.c +++ b/fs/nfs/pagelist.c | |||
@@ -117,7 +117,7 @@ __nfs_iocounter_wait(struct nfs_io_counter *c) | |||
117 | set_bit(NFS_IO_INPROGRESS, &c->flags); | 117 | set_bit(NFS_IO_INPROGRESS, &c->flags); |
118 | if (atomic_read(&c->io_count) == 0) | 118 | if (atomic_read(&c->io_count) == 0) |
119 | break; | 119 | break; |
120 | ret = nfs_wait_bit_killable(&c->flags); | 120 | ret = nfs_wait_bit_killable(&q.key); |
121 | } while (atomic_read(&c->io_count) != 0); | 121 | } while (atomic_read(&c->io_count) != 0); |
122 | finish_wait(wq, &q.wait); | 122 | finish_wait(wq, &q.wait); |
123 | return ret; | 123 | return ret; |