From: David Howells dhowells@redhat.com
[ Upstream commit 03275585cabd0240944f19f33d7584a1b099a3a8 ]
When an AFS FS.StoreData RPC call is made, amongst other things it is given the resultant file size to be. On the server, this is processed by truncating the file to new size and then writing the data.
Now, kafs has a lock (vnode->io_lock) that serves to serialise operations against a specific vnode (ie. inode), but the parameters for the op are set before the lock is taken. This allows two writebacks (say sync and kswapd) to race - and if writes are ongoing the writeback for a later write could occur before the writeback for an earlier one if the latter gets interrupted.
Note that afs_writepages() cannot take i_mutex and only takes a shared lock on vnode->validate_lock.
Also note that the server does the truncation and the write inside a lock, so there's no problem at that end.
Fix this by moving the calculation for the proposed new i_size inside the vnode->io_lock. Also reset the iterator (which we might have read from) and update the mtime setting there.
Fixes: bd80d8a80e12 ("afs: Use ITER_XARRAY for writing") Reported-by: Marc Dionne marc.dionne@auristor.com Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Jeffrey Altman jaltman@auristor.com Reviewed-by: Marc Dionne marc.dionne@auristor.com cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/3526895.1687960024@warthog.procyon.org.uk/ Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/afs/write.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/afs/write.c b/fs/afs/write.c index 8750b99c3f566..c1f4391ccd7c6 100644 --- a/fs/afs/write.c +++ b/fs/afs/write.c @@ -413,17 +413,19 @@ static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t afs_op_set_vnode(op, 0, vnode); op->file[0].dv_delta = 1; op->file[0].modification = true; - op->store.write_iter = iter; op->store.pos = pos; op->store.size = size; - op->store.i_size = max(pos + size, vnode->netfs.remote_i_size); op->store.laundering = laundering; - op->mtime = vnode->netfs.inode.i_mtime; op->flags |= AFS_OPERATION_UNINTR; op->ops = &afs_store_data_operation;
try_next_key: afs_begin_vnode_operation(op); + + op->store.write_iter = iter; + op->store.i_size = max(pos + size, vnode->netfs.remote_i_size); + op->mtime = vnode->netfs.inode.i_mtime; + afs_wait_for_operation(op);
switch (op->error) {