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authorNeilBrown <neilb@suse.de>2014-07-07 01:16:04 -0400
committerIngo Molnar <mingo@kernel.org>2014-07-16 09:10:41 -0400
commitc1221321b7c25b53204447cff9949a6d5a7ddddc (patch)
treeb4dc6613ab838dcd71023f5f018306574fc2985a /fs/nfs/pagelist.c
parent743162013d40ca612b4cb53d3a200dff2d9ab26e (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.c2
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;