afs: Introduce afs_kill_pending()

Introduce a function that checks to see if the current kernel task has
a pending kill (e.g. SIGKILL) that will terminate the process when it
returns to userspace.

Add afs_kill_pending() that uses an osi level function,
osi_kill_pending() to determine if the process has a pending
termination. If the osi level function has not been implemented, just
return 0.

Add a Linux implementation of osi_kill_pending() that calls Linux's
fatal_signal_pending() (if it's available).

Update Linux's "filter_enoent()" function in osi_vnodeops.c to use
afs_kill_pending().

A future commit will expand the use of afs_kill_pending().

Fix minor white space in an adjacent lines.

Change-Id: Ib215639d36f4baa7a1dffda3cc314d2d447c6e96
Reviewed-on: https://gerrit.openafs.org/15746
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>

src/afs/LINUX/osi_misc.c

@@ -186,3 +186,20 @@ afs_start_thread(void (*proc)(void), char *name, int needs_glock)
 	kthread_run(afs_thread_wrapper, proc, "%s", name);
     }
 }
+
+/*
+ * Check for a pending fatal signal
+ * Return 1 if a fatal signal is pending, otherwise return 0;
+ */
+int
+osi_kill_pending(void)
+{
+#if defined(HAVE_LINUX_FATAL_SIGNAL_PENDING)
+    if (fatal_signal_pending(current)) {
+	return 1;
+    }
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,25)
+# error fatal_signal_pending not available, but it should be
+#endif
+    return 0;
+}

src/afs/LINUX/osi_prototypes.h

@@ -51,6 +51,7 @@ extern int osi_lookupname(char *aname, uio_seg_t seg, int followlink,
 extern int osi_abspath(char *aname, char *buf, int buflen,
 		       int followlink, char **pathp);
 extern void afs_start_thread(void (*proc)(void), char *name, int needs_glock);
+extern int osi_kill_pending(void);
 
 /* osi_probe.c */
 extern void *osi_find_syscall_table(int which);

src/afs/LINUX/osi_vnodeops.c

@@ -1305,17 +1305,19 @@ parent_vcache_dv(struct inode *inode, cred_t *credp)
     }
     return hgetlo(pvcp->f.m.DataVersion);
 }
-
+/*
+ * Make sure we don't accidentally yield an ENOENT that's caused by internal
+ * errors instead of the requested filename actually not existing. This has been
+ * possible in the past because Linux returns errors for some low-level routines
+ * when the process is dying. Incorrect ENOENT errors can cause bogus negative
+ * dentries to exist, which is very bad, so make sure that doesn't happen.
+ */
 static inline int
 filter_enoent(int code)
 {
-#ifdef HAVE_LINUX_FATAL_SIGNAL_PENDING
-    if (code == ENOENT && fatal_signal_pending(current)) {
-        return EINTR;
+    if (code == ENOENT && afs_kill_pending()) {
+	return EINTR;
     }
-#elif LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,25)
-# error fatal_signal_pending not available, but it should be
-#endif
     return code;
 }
 

src/afs/afs_analyze.c

@@ -383,6 +383,38 @@ afs_PrintServerErrors(struct vrequest *areq, struct VenusFid *afid)
     afs_warnuser("%s\n", term);
 }
 
+/*!
+ * \brief
+ *	Determine if the current process is pending termination and will be
+ *	killed when returning to userspace.
+ *
+ * \retval 1 if the process is dying
+ * \retval 0 if the process is not dying
+ *
+ * \note
+ *	If the process is pending termination, there is no need to retry requests
+ *	or wait for a server to return data, etc. as the process is going to die
+ *	before it can process any data.  However we will still need to ensure that
+ *	we don't corrupt any locks, cache, etc., or any data that persists in other
+ *	processes.
+ *
+ * \note
+ *	On some platforms (Linux), a process will not sleep if it is pending
+ *	termination.  If we can detect that the process will be killed, it is better
+ *	to not retry the requests, etc. to avoid spinning the CPU.
+ */
+int
+afs_kill_pending(void)
+{
+#if defined(UKERNEL)
+    return 0;
+#elif defined(AFS_LINUX_ENV)
+    return osi_kill_pending();
+#else
+    return 0;
+#endif /* UKERNEL */
+}
+
 /*!
  * \brief
  *	Analyze the outcome of an RPC operation, taking whatever support

src/afs/afs_prototypes.h

@@ -11,9 +11,10 @@
 #define _AFS_PROTOTYPES_H_
 
 /* afs_analyze.c */
+extern int afs_kill_pending(void);
 extern int afs_Analyze(struct afs_conn *aconn, struct rx_connection *rxconn,
-                       afs_int32 acode, struct VenusFid *afid,
-                       struct vrequest *areq,
+		       afs_int32 acode, struct VenusFid *afid,
+		       struct vrequest *areq,
 		       int op, afs_int32 locktype, struct cell *cellp);
 
 /* afs_axscache.c */