smb3: add way to control slow response threshold for logging and stats

/proc/fs/cifs/Stats when CONFIG_CIFS_STATS2 is enabled logs 'slow'
responses, but depending on the server you are debugging a
one second timeout may be too fast, so allow setting it to
a larger number of seconds via new module parameter

/sys/module/cifs/parameters/slow_rsp_threshold

or via modprobe:

slow_rsp_threshold:Amount of time (in seconds) to wait before
logging that a response is delayed.
Default: 1 (if set to 0 disables msg). (uint)

Recommended values are 0 (disabled) to 32767 (9 hours) with
the default remaining as 1 second.
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>

fs/cifs/cifsfs.c

@@ -81,6 +81,14 @@ module_param(cifs_max_pending, uint, 0444);
 MODULE_PARM_DESC(cifs_max_pending, "Simultaneous requests to server for "
 				   "CIFS/SMB1 dialect (N/A for SMB3) "
 				   "Default: 32767 Range: 2 to 32767.");
+#ifdef CONFIG_CIFS_STATS2
+unsigned int slow_rsp_threshold = 1;
+module_param(slow_rsp_threshold, uint, 0644);
+MODULE_PARM_DESC(slow_rsp_threshold, "Amount of time (in seconds) to wait "
+				   "before logging that a response is delayed. "
+				   "Default: 1 (if set to 0 disables msg).");
+#endif /* STATS2 */
+
 module_param(enable_oplocks, bool, 0644);
 MODULE_PARM_DESC(enable_oplocks, "Enable or disable oplocks. Default: y/Y/1");
 
@@ -1418,6 +1426,11 @@ init_cifs(void)
 #ifdef CONFIG_CIFS_STATS2
 	atomic_set(&totBufAllocCount, 0);
 	atomic_set(&totSmBufAllocCount, 0);
+	if (slow_rsp_threshold < 1)
+		cifs_dbg(FYI, "slow_response_threshold msgs disabled\n");
+	else if (slow_rsp_threshold > 32767)
+		cifs_dbg(VFS,
+		       "slow response threshold set higher than recommended (0 to 32767)\n");
 #endif /* CONFIG_CIFS_STATS2 */
 
 	atomic_set(&midCount, 0);

fs/cifs/cifsglob.h

@@ -1715,6 +1715,7 @@ GLOBAL_EXTERN atomic_t bufAllocCount;    /* current number allocated  */
 #ifdef CONFIG_CIFS_STATS2
 GLOBAL_EXTERN atomic_t totBufAllocCount; /* total allocated over all time */
 GLOBAL_EXTERN atomic_t totSmBufAllocCount;
+extern unsigned int slow_rsp_threshold; /* number of secs before logging */
 #endif
 GLOBAL_EXTERN atomic_t smBufAllocCount;
 GLOBAL_EXTERN atomic_t midCount;

fs/cifs/transport.c

@@ -113,9 +113,18 @@ DeleteMidQEntry(struct mid_q_entry *midEntry)
 		cifs_small_buf_release(midEntry->resp_buf);
 #ifdef CONFIG_CIFS_STATS2
 	now = jiffies;
-	/* commands taking longer than one second are indications that
-	   something is wrong, unless it is quite a slow link or server */
-	if (time_after(now, midEntry->when_alloc + HZ) &&
+	/*
+	 * commands taking longer than one second (default) can be indications
+	 * that something is wrong, unless it is quite a slow link or a very
+	 * busy server. Note that this calc is unlikely or impossible to wrap
+	 * as long as slow_rsp_threshold is not set way above recommended max
+	 * value (32767 ie 9 hours) and is generally harmless even if wrong
+	 * since only affects debug counters - so leaving the calc as simple
+	 * comparison rather than doing multiple conversions and overflow
+	 * checks
+	 */
+	if ((slow_rsp_threshold != 0) &&
+	    time_after(now, midEntry->when_alloc + (slow_rsp_threshold * HZ)) &&
 	    (midEntry->command != command)) {
 		/* smb2slowcmd[NUMBER_OF_SMB2_COMMANDS] counts by command */
 		if ((le16_to_cpu(midEntry->command) < NUMBER_OF_SMB2_COMMANDS) &&