[MEH PATCH] fs: sort out a stale comment about races between fd alloc and dup2

[Mateusz Guzik <mjguzik@gmail.com>]

It claims the issue is only relevant for shared descriptor tables which
is of no concern for POSIX (but then is POSIX of concern to anyone
today?), which I presume predates standarized threading.

The comment also mentions the following systems:
- OpenBSD installing a larval file -- this remains accurate
- FreeBSD returning EBADF -- not accurate, the system uses the same
  idea as OpenBSD
- NetBSD "deadlocks in amusing ways" -- their solution looks
  Solaris-inspired (not a compliment) and I would not be particularly
  surprised if it indeed deadlocked, in amusing ways or otherwise

I don't believe mentioning any of these adds anything and the statement
about the issue not being POSIX-relevant is outdated.

dup2 description in POSIX still does not mention the problem.

Just shorten the comment and be done with it.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---

I'm pretty sure the comment adds nothing in the current form, but I'm
not going to argue about it.

 fs/file.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index d065a24980da..ad8aabc08122 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1258,17 +1258,9 @@ __releases(&files->file_lock)
 
 	/*
 	 * We need to detect attempts to do dup2() over allocated but still
-	 * not finished descriptor.  NB: OpenBSD avoids that at the price of
-	 * extra work in their equivalent of fget() - they insert struct
-	 * file immediately after grabbing descriptor, mark it larval if
-	 * more work (e.g. actual opening) is needed and make sure that
-	 * fget() treats larval files as absent.  Potentially interesting,
-	 * but while extra work in fget() is trivial, locking implications
-	 * and amount of surgery on open()-related paths in VFS are not.
-	 * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
-	 * deadlocks in rather amusing ways, AFAICS.  All of that is out of
-	 * scope of POSIX or SUS, since neither considers shared descriptor
-	 * tables and this condition does not arise without those.
+	 * not finished descriptor.
+	 *
+	 * POSIX is silent on the issue, we return -EBUSY.
 	 */
 	fdt = files_fdtable(files);
 	fd = array_index_nospec(fd, fdt->max_fds);
-- 
2.43.0