Re: [PATCH 2/9] vfs: export do_splice_direct() to modules

From: J. R. Okajima
Date: Fri Mar 22 2013 - 22:49:21 EST

Al Viro:
> The scenario, BTW, looks so:
> process A does sb_start_write() (on your upper layer)
> process B tries to freeze said upper layer and blocks, waiting for A to finish
> process C grabs ->i_mutex in your upper layer
> process C does vfs_write(), which blocks, since there's a pending attempt to
> freeze
> process A tries to grab ->i_mutex held by C and blocks

According to latest mm/filemap.c:generic_file_aio_write(),
ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);

Process C would block *BEFORE* i_mutex by sb_start_write()? No?
Honestly speaking I didn't pay attention about the freeze feature since
I don't use it. I am making aufs to support it now. But I don't know how
to test it...

J. R. Okajima
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