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Date:      Thu, 6 Jul 2017 15:03:54 +0000 (UTC)
From:      Andrew Gallatin <gallatin@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r320738 - head/sys/kern
Message-ID:  <201707061503.v66F3s3p055733@repo.freebsd.org>
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Author: gallatin
Date: Thu Jul  6 15:03:54 2017
New Revision: 320738
URL: https://svnweb.freebsd.org/changeset/base/320738

Log:
  Simplify UIO_SYSSPACE and UIO_NOCOPY paths in uiomove
  
  Uiomove can only block when the segflag is UIO_USERSPACE,
  otherwise we end up just doing a bcopy (or nothing) and
  moving cursors. So only emit witness warnings and
  set deadlock thread flags in the UIO_USERSPACE case.
  
  Reviewed by:	kib
  Sponsored by:	Netflix
  Differential Revision:	https://reviews.freebsd.org/D11489

Modified:
  head/sys/kern/subr_uio.c

Modified: head/sys/kern/subr_uio.c
==============================================================================
--- head/sys/kern/subr_uio.c	Thu Jul  6 14:47:59 2017	(r320737)
+++ head/sys/kern/subr_uio.c	Thu Jul  6 15:03:54 2017	(r320738)
@@ -206,31 +206,32 @@ uiomove_nofault(void *cp, int n, struct uio *uio)
 static int
 uiomove_faultflag(void *cp, int n, struct uio *uio, int nofault)
 {
-	struct thread *td;
 	struct iovec *iov;
 	size_t cnt;
 	int error, newflags, save;
 
-	td = curthread;
 	error = 0;
 
 	KASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE,
 	    ("uiomove: mode"));
-	KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_td == td,
+	KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_td == curthread,
 	    ("uiomove proc"));
-	if (!nofault)
-		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
-		    "Calling uiomove()");
 
-	/* XXX does it make a sense to set TDP_DEADLKTREAT for UIO_SYSSPACE ? */
-	newflags = TDP_DEADLKTREAT;
-	if (uio->uio_segflg == UIO_USERSPACE && nofault) {
-		/*
-		 * Fail if a non-spurious page fault occurs.
-		 */
-		newflags |= TDP_NOFAULTING | TDP_RESETSPUR;
+	if (uio->uio_segflg == UIO_USERSPACE) {
+		newflags = TDP_DEADLKTREAT;
+		if (nofault) {
+			/*
+			 * Fail if a non-spurious page fault occurs.
+			 */
+			newflags |= TDP_NOFAULTING | TDP_RESETSPUR;
+		} else {
+			WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
+			    "Calling uiomove()");
+		}
+		save = curthread_pflags_set(newflags);
+	} else {
+		KASSERT(nofault == 0, ("uiomove: nofault"));
 	}
-	save = curthread_pflags_set(newflags);
 
 	while (n > 0 && uio->uio_resid) {
 		iov = uio->uio_iov;
@@ -272,7 +273,8 @@ uiomove_faultflag(void *cp, int n, struct uio *uio, in
 		n -= cnt;
 	}
 out:
-	curthread_pflags_restore(save);
+	if (uio->uio_segflg == UIO_USERSPACE) 
+		curthread_pflags_restore(save);
 	return (error);
 }

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