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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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| .. | ||
| asn1.c | ||
| cache.c | ||
| cifs_debug.c | ||
| cifs_debug.h | ||
| cifs_dfs_ref.c | ||
| cifs_fs_sb.h | ||
| cifs_spnego.c | ||
| cifs_spnego.h | ||
| cifs_unicode.c | ||
| cifs_unicode.h | ||
| cifs_uniupr.h | ||
| cifsacl.c | ||
| cifsacl.h | ||
| cifsencrypt.c | ||
| cifsfs.c | ||
| cifsfs.h | ||
| cifsglob.h | ||
| cifspdu.h | ||
| cifsproto.h | ||
| cifssmb.c | ||
| connect.c | ||
| dir.c | ||
| dns_resolve.c | ||
| dns_resolve.h | ||
| export.c | ||
| file.c | ||
| fscache.c | ||
| fscache.h | ||
| inode.c | ||
| ioctl.c | ||
| Kconfig | ||
| link.c | ||
| Makefile | ||
| misc.c | ||
| netmisc.c | ||
| nterr.c | ||
| nterr.h | ||
| ntlmssp.h | ||
| readdir.c | ||
| rfc1002pdu.h | ||
| sess.c | ||
| smb1ops.c | ||
| smb2file.c | ||
| smb2glob.h | ||
| smb2inode.c | ||
| smb2maperror.c | ||
| smb2misc.c | ||
| smb2ops.c | ||
| smb2pdu.c | ||
| smb2pdu.h | ||
| smb2proto.h | ||
| smb2status.h | ||
| smb2transport.c | ||
| smbencrypt.c | ||
| smberr.h | ||
| smbfsctl.h | ||
| transport.c | ||
| winucase.c | ||
| xattr.c | ||