posix record locking?

posix record locking?

[moiz kohari]

Hi,

I am looking at posix record locking with nfs and I have a couple of 
questions:

1. The fcntl_setlk() calls nfs_lock() (towards the end of fcntl_setlk by 
calling filp->f_op->lock), fcntl_setlk() then calls posix_lock_file() 
(where all the vfs magic happens for file locks).  If nfs_lock() returns 
successful (server has granted the lock) but the subsequent 
posix_lock_file() fails (due to deadlock, conflict or low memory), we 
never go back to the server to clean up this lock.  Is this a problem or 
am I missing something?

2. nfs_lock() calls nlmclnt_proc() after we pick up the kernel lock 
(lock_kernel()).  The nlmclnt_proc() goes on to call:
    nlmclnt_lock()
    nlmclnt_call()
    rpc...

Is this OK?  Are we going over the wire while holding the kernel lock?

Thanks for your help and please cc my email on any responses.

Best Regards,

Moiz




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Re: posix record locking?

[Trond Myklebust]

>>>>> " " == moiz kohari <moiz_kohari@yahoo.com> writes:

     > Hi, I am looking at posix record locking with nfs and I have a
     > couple of questions:


     > 1. The fcntl_setlk() calls nfs_lock() (towards the end of fcntl_setlk
     >    by calling filp->f_op->lock), fcntl_setlk() then calls
     >    posix_lock_file() (where all the vfs magic happens for file
     >    locks).  If nfs_lock() returns successful (server has
     >    granted the lock) but the subsequent posix_lock_file() fails
     >    (due to deadlock, conflict or low memory), we never go back
     >    to the server to clean up this lock.  Is this a problem or
     >    am I missing something?


Low memory is a problem, but how are you going to solve that (RPC
calls require memory too)?

As for the rest: why would the VFS tell us we're
deadlocked/conflicting if the server says we aren't? That would
clearly be a bug.

     > 2. nfs_lock() calls nlmclnt_proc() after we pick up the kernel lock
     >    (lock_kernel()).  The nlmclnt_proc() goes on to call:

     >     nlmclnt_lock() nlmclnt_call() rpc...

     > Is this OK?  Are we going over the wire while holding the
     > kernel lock?

Yes. The BKL is unique as far as spinlocks go in that it allows this
sort of thing.

Cheers,
  Trond


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