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c1221321b7
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>
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| .. | ||
| blocklayout | ||
| filelayout | ||
| objlayout | ||
| cache_lib.c | ||
| cache_lib.h | ||
| callback_proc.c | ||
| callback_xdr.c | ||
| callback.c | ||
| callback.h | ||
| client.c | ||
| delegation.c | ||
| delegation.h | ||
| dir.c | ||
| direct.c | ||
| dns_resolve.c | ||
| dns_resolve.h | ||
| file.c | ||
| fscache-index.c | ||
| fscache.c | ||
| fscache.h | ||
| getroot.c | ||
| idmap.c | ||
| inode.c | ||
| internal.h | ||
| iostat.h | ||
| Kconfig | ||
| Makefile | ||
| mount_clnt.c | ||
| namespace.c | ||
| netns.h | ||
| nfs2super.c | ||
| nfs2xdr.c | ||
| nfs3acl.c | ||
| nfs3client.c | ||
| nfs3proc.c | ||
| nfs3super.c | ||
| nfs3xdr.c | ||
| nfs4_fs.h | ||
| nfs4client.c | ||
| nfs4file.c | ||
| nfs4getroot.c | ||
| nfs4namespace.c | ||
| nfs4proc.c | ||
| nfs4renewd.c | ||
| nfs4session.c | ||
| nfs4session.h | ||
| nfs4state.c | ||
| nfs4super.c | ||
| nfs4sysctl.c | ||
| nfs4trace.c | ||
| nfs4trace.h | ||
| nfs4xdr.c | ||
| nfs.h | ||
| nfsroot.c | ||
| nfstrace.c | ||
| nfstrace.h | ||
| pagelist.c | ||
| pnfs_dev.c | ||
| pnfs.c | ||
| pnfs.h | ||
| proc.c | ||
| read.c | ||
| super.c | ||
| symlink.c | ||
| sysctl.c | ||
| unlink.c | ||
| write.c | ||