git: 45bb8beacc2f - main - fd: elide one acquire fence in fget_unlocked_seq

The branch main has been updated by mjg:

URL: https://cgit.FreeBSD.org/src/commit/?id=45bb8beacc2fadbbc32428df0f2f5683863df289

commit 45bb8beacc2fadbbc32428df0f2f5683863df289
Author:     Mateusz Guzik <mjg@FreeBSD.org>
AuthorDate: 2022-02-01 16:58:12 +0000
Commit:     Mateusz Guzik <mjg@FreeBSD.org>
CommitDate: 2022-02-11 12:29:26 +0000

    fd: elide one acquire fence in fget_unlocked_seq
    
    Still validate we got the stable state before returning an error though.
---
 sys/kern/kern_descrip.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index c4f435002907..e5ffdb01255f 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -3060,13 +3060,19 @@ fget_unlocked_seq(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
 		fde = &fdt->fdt_ofiles[fd];
 		haverights = *cap_rights_fde_inline(fde);
 		fp = fde->fde_file;
-		if (!seqc_consistent(fd_seqc(fdt, fd), seq))
+		if (__predict_false(fp == NULL)) {
+			if (seqc_consistent(fd_seqc(fdt, fd), seq))
+				return (EBADF);
+			fdt = atomic_load_ptr(&fdp->fd_files);
 			continue;
-		if (__predict_false(fp == NULL))
-			return (EBADF);
+		}
 		error = cap_check_inline(&haverights, needrightsp);
-		if (__predict_false(error != 0))
-			return (error);
+		if (__predict_false(error != 0)) {
+			if (seqc_consistent(fd_seqc(fdt, fd), seq))
+				return (error);
+			fdt = atomic_load_ptr(&fdp->fd_files);
+			continue;
+		}
 		if (__predict_false(!refcount_acquire_if_not_zero(&fp->f_count))) {
 			fdt = atomic_load_ptr(&fdp->fd_files);
 			continue;