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Date:      Fri, 2 Jun 2017 16:52:18 +0000 (UTC)
From:      Hans Petter Selasky <hselasky@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r319501 - head/sys/compat/linuxkpi/common/src
Message-ID:  <201706021652.v52GqIS7028920@repo.freebsd.org>
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Author: hselasky
Date: Fri Jun  2 16:52:18 2017
New Revision: 319501
URL: https://svnweb.freebsd.org/changeset/base/319501

Log:
  Improve kqueue() support in the LinuxKPI. Some applications using the
  kqueue() does not set non-blocking I/O mode for event driven read of
  file descriptors. This means the LinuxKPI internal kqueue read and
  write event flags must be updated before the next read and/or write
  system call. Else the read and/or write system call may block. This
  can happen when there is no more data to read following a previous
  read event. Then the application also gets blocked from processing
  other events. This situation can also be solved by the applications
  setting and using non-blocking I/O mode.
  
  MFC after:		1 week
  Sponsored by:		Mellanox Technologies

Modified:
  head/sys/compat/linuxkpi/common/src/linux_compat.c

Modified: head/sys/compat/linuxkpi/common/src/linux_compat.c
==============================================================================
--- head/sys/compat/linuxkpi/common/src/linux_compat.c	Fri Jun  2 16:30:40 2017	(r319500)
+++ head/sys/compat/linuxkpi/common/src/linux_compat.c	Fri Jun  2 16:52:18 2017	(r319501)
@@ -438,7 +438,7 @@ linux_kq_lock_unowned(void *arg)
 }
 
 static void
-linux_dev_kqfilter_poll(struct linux_file *);
+linux_dev_kqfilter_poll(struct linux_file *, int);
 
 struct linux_file *
 linux_file_alloc(void)
@@ -856,9 +856,11 @@ linux_dev_ioctl(struct cdev *dev, u_long cmd, caddr_t 
 		current->bsd_ioctl_len = 0;
 	}
 
-	if (error == EWOULDBLOCK)
-		linux_dev_kqfilter_poll(filp);
-	else if (error == ERESTARTSYS)
+	if (error == EWOULDBLOCK) {
+		/* update kqfilter status, if any */
+		linux_dev_kqfilter_poll(filp,
+		    LINUX_KQ_FLAG_HAS_READ | LINUX_KQ_FLAG_HAS_WRITE);
+	} else if (error == ERESTARTSYS)
 		error = ERESTART;
 	return (error);
 }
@@ -893,14 +895,15 @@ linux_dev_read(struct cdev *dev, struct uio *uio, int 
 			uio->uio_resid -= bytes;
 		} else {
 			error = -bytes;
-			if (error == EWOULDBLOCK)
-				linux_dev_kqfilter_poll(filp);
-			else if (error == ERESTARTSYS)
+			if (error == ERESTARTSYS)
 				error = ERESTART;
 		}
 	} else
 		error = ENXIO;
 
+	/* update kqfilter status, if any */
+	linux_dev_kqfilter_poll(filp, LINUX_KQ_FLAG_HAS_READ);
+
 	return (error);
 }
 
@@ -934,14 +937,15 @@ linux_dev_write(struct cdev *dev, struct uio *uio, int
 			uio->uio_resid -= bytes;
 		} else {
 			error = -bytes;
-			if (error == EWOULDBLOCK)
-				linux_dev_kqfilter_poll(filp);
-			else if (error == ERESTARTSYS)
+			if (error == ERESTARTSYS)
 				error = ERESTART;
 		}
 	} else
 		error = ENXIO;
 
+	/* update kqfilter status, if any */
+	linux_dev_kqfilter_poll(filp, LINUX_KQ_FLAG_HAS_WRITE);
+
 	return (error);
 }
 
@@ -1032,21 +1036,20 @@ static struct filterops linux_dev_kqfiltops_write = {
 };
 
 static void
-linux_dev_kqfilter_poll(struct linux_file *filp)
+linux_dev_kqfilter_poll(struct linux_file *filp, int kqflags)
 {
 	int temp;
 
-	spin_lock(&filp->f_kqlock);
-	temp = (filp->f_kqflags & (LINUX_KQ_FLAG_HAS_READ | LINUX_KQ_FLAG_HAS_WRITE));
-	filp->f_kqflags &= ~(LINUX_KQ_FLAG_NEED_READ | LINUX_KQ_FLAG_NEED_WRITE);
-	spin_unlock(&filp->f_kqlock);
-
-	if (temp != 0) {
+	if (filp->f_kqflags & kqflags) {
 		/* get the latest polling state */
 		temp = filp->f_op->poll(filp, NULL);
 
+		spin_lock(&filp->f_kqlock);
+		/* clear kqflags */
+		filp->f_kqflags &= ~(LINUX_KQ_FLAG_NEED_READ |
+		    LINUX_KQ_FLAG_NEED_WRITE);
+		/* update kqflags */
 		if (temp & (POLLIN | POLLOUT)) {
-			spin_lock(&filp->f_kqlock);
 			if (temp & POLLIN)
 				filp->f_kqflags |= LINUX_KQ_FLAG_NEED_READ;
 			if (temp & POLLOUT)
@@ -1054,8 +1057,8 @@ linux_dev_kqfilter_poll(struct linux_file *filp)
 
 			/* make sure the "knote" gets woken up */
 			KNOTE_LOCKED(&filp->f_selinfo.si_note, 0);
-			spin_unlock(&filp->f_kqlock);
 		}
+		spin_unlock(&filp->f_kqlock);
 	}
 }
 
@@ -1099,7 +1102,10 @@ linux_dev_kqfilter(struct cdev *dev, struct knote *kn)
 
 	if (error == 0) {
 		linux_set_current(td);
-		linux_dev_kqfilter_poll(filp);
+
+		/* update kqfilter status, if any */
+		linux_dev_kqfilter_poll(filp,
+		    LINUX_KQ_FLAG_HAS_READ | LINUX_KQ_FLAG_HAS_WRITE);
 	}
 	return (error);
 }

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