Concurrent nfs_service() call and nfs_lstat64_async() calls

[haihon...@rubrik.com]

I wonder if libnfs is safe if I have code like this: one thread is doing poll()/nfs_service() to process NFS responses, another thread calls nfs_lstat64_async() simultaneously. Is there threading issue with this model?

[ronnie sahlberg]

It is not safe since when you call nfs_lstat64_async() as it will
modify the nfs_context linked list of pointers for the queue of
outgoing PDUs.
That same list is also read and modified in nfs_service() when it
writes a queued PDU to the wire.


You need to wrap these calls inside a mutex. That should not harm
performance much/any-at-all in modern linux which uses futex-es as the
mutex primitive.
As nfs_lstat64_async is guaranteed to be non-blocking and thus will
return almost instantly, there will not be much/any-at-all impact of
the serialization that this futex would incur.

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