On Thu, Dec 21, 2023 at 01:23:10PM +0000, David Howells wrote: > Add a bvec array pointer and an iterator to netfs_io_request for either > holding a copy of a DIO iterator or a list of all the bits of buffer > pointed to by a DIO iterator. > > There are two problems: Firstly, if an iovec-class iov_iter is passed to > ->read_iter() or ->write_iter(), this cannot be passed directly to > kernel_sendmsg() or kernel_recvmsg() as that may cause locking recursion if > a fault is generated, so we need to keep track of the pages involved > separately. > > Secondly, if the I/O is asynchronous, we must copy the iov_iter describing > the buffer before returning to the caller as it may be immediately > deallocated. > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> > cc: linux-cachefs@xxxxxxxxxx > cc: linux-fsdevel@xxxxxxxxxxxxxxx > cc: linux-mm@xxxxxxxxx > --- > fs/netfs/objects.c | 10 ++++++++++ > include/linux/netfs.h | 4 ++++ > 2 files changed, 14 insertions(+) > > diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c > index 1bd20bdad983..4df5e5eeada6 100644 > --- a/fs/netfs/objects.c > +++ b/fs/netfs/objects.c > @@ -76,6 +76,7 @@ static void netfs_free_request(struct work_struct *work) > { > struct netfs_io_request *rreq = > container_of(work, struct netfs_io_request, work); > + unsigned int i; > > trace_netfs_rreq(rreq, netfs_rreq_trace_free); > netfs_proc_del_rreq(rreq); > @@ -84,6 +85,15 @@ static void netfs_free_request(struct work_struct *work) > rreq->netfs_ops->free_request(rreq); > if (rreq->cache_resources.ops) > rreq->cache_resources.ops->end_operation(&rreq->cache_resources); > + if (rreq->direct_bv) { > + for (i = 0; i < rreq->direct_bv_count; i++) { > + if (rreq->direct_bv[i].bv_page) { > + if (rreq->direct_bv_unpin) > + unpin_user_page(rreq->direct_bv[i].bv_page); > + } > + } > + kvfree(rreq->direct_bv); > + } > kfree_rcu(rreq, rcu); > netfs_stat_d(&netfs_n_rh_rreq); > } > diff --git a/include/linux/netfs.h b/include/linux/netfs.h > index 3da962e977f5..bbb33ccbf719 100644 > --- a/include/linux/netfs.h > +++ b/include/linux/netfs.h > @@ -190,6 +190,9 @@ struct netfs_io_request { > struct iov_iter iter; /* Unencrypted-side iterator */ > struct iov_iter io_iter; /* I/O (Encrypted-side) iterator */ > void *netfs_priv; /* Private data for the netfs */ > + struct bio_vec *direct_bv /* DIO buffer list (when handling iovec-iter) */ > + __counted_by(direct_bv_count); This will break the build with versions of clang that have support for counted_by (as it has been reverted in main but reapplication to main is being actively worked on) because while annotating pointers with this attribute is a goal of the counted_by attribute, it is not ready yet. Please consider removing this and adding a TODO to annotate it when support is available. In file included from /builds/linux/fs/ceph/crypto.c:14: In file included from /builds/linux/fs/ceph/super.h:20: /builds/linux/include/linux/netfs.h:259:19: error: 'counted_by' only applies to C99 flexible array members 259 | struct bio_vec *direct_bv /* DIO buffer list (when handling iovec-iter) */ | ^~~~~~~~~ 1 error generated. Some additional context from another recent error like this: https://lore.kernel.org/CAKwvOdkvGTGiWzqEFq=kzqvxSYP5vUj3g9Z-=MZSQROzzSa_dg@xxxxxxxxxxxxxx/ Cheers, Nathan > + unsigned int direct_bv_count; /* Number of elements in direct_bv[] */ > unsigned int debug_id; > atomic_t nr_outstanding; /* Number of ops in progress */ > atomic_t nr_copy_ops; /* Number of copy-to-cache ops in progress */ > @@ -197,6 +200,7 @@ struct netfs_io_request { > size_t len; /* Length of the request */ > short error; /* 0 or error that occurred */ > enum netfs_io_origin origin; /* Origin of the request */ > + bool direct_bv_unpin; /* T if direct_bv[] must be unpinned */ > loff_t i_size; /* Size of the file */ > loff_t start; /* Start position */ > pgoff_t no_unlock_folio; /* Don't unlock this folio after read */ >