From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> I originally set out to make netfs_perform_write() behavior more consistent with generic_perform_write(). However, netfs currently treats a failure to make forward progress as a hard error and does not retry where the generic code will loop around and retry. Instead of a major code restructuring, just focus on improving the comments. The comment refers to a possible deadlock and to userspace address checks. Neither of those things are a concern when using copy_folio_from_iter_atomic() for atomic usercopies. It prevents deadlocks by disabling page faults and it leverages user copy functions that have their own access_ok() checks. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: David Howells <dhowells@xxxxxxxxxx> Cc: Jeff Layton <jlayton@xxxxxxxxxx> Cc: netfs@xxxxxxxxxxxxxxx --- b/fs/netfs/buffered_write.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) diff -puN fs/netfs/buffered_write.c~netfs-postfault fs/netfs/buffered_write.c --- a/fs/netfs/buffered_write.c~netfs-postfault 2025-01-29 09:03:38.167859749 -0800 +++ b/fs/netfs/buffered_write.c 2025-01-29 09:03:38.171860082 -0800 @@ -152,16 +152,9 @@ ssize_t netfs_perform_write(struct kiocb offset = pos & (max_chunk - 1); part = min(max_chunk - offset, iov_iter_count(iter)); - /* Bring in the user pages that we will copy from _first_ lest - * we hit a nasty deadlock on copying from the same page as - * we're writing to, without it being marked uptodate. - * - * Not only is this an optimisation, but it is also required to - * check that the address is actually valid, when atomic - * usercopies are used below. - * - * We rely on the page being held onto long enough by the LRU - * that we can grab it below if this causes it to be read. + /* Bring in the user folios that are copied from before taking + * locks on the mapping folios. This helps ensure forward + * progress if they are the same folios. */ ret = -EFAULT; if (unlikely(fault_in_iov_iter_readable(iter, part) == part)) _
