[REVIEW] Move memory allocations for log tracing out of the critical path

[Lachlan McIlroy <lachlan@xxxxxxx>]

Memory allocations for log->l_grant_trace and iclog->ic_trace are done
on demand when the first event is logged.  In xlog_state_get_iclog_space()
we call xlog_trace_iclog() under a spinlock and allocating memory here can
cause us to sleep with a spinlock held and deadlock the system.

For the log grant tracing we use KM_NOSLEEP but that means we can lose
trace entries.  Since there is no locking to serialize the log grant
tracing we could race and have multiple allocations and leak memory.

So move the allocations to where we initialize the log/iclog structures.
Use KM_NOFS to avoid recursing into the filesystem and drop log->l_trace
since it's not even used.

Index: 2.6.x-clean/fs/xfs/xfs_log.c
===================================================================
--- 2.6.x-clean.orig/fs/xfs/xfs_log.c
+++ 2.6.x-clean/fs/xfs/xfs_log.c
@@ -124,16 +124,27 @@ STATIC void	xlog_verify_tail_lsn(xlog_t 
STATIC int	xlog_iclogs_empty(xlog_t *log);

#if defined(XFS_LOG_TRACE)
+
+#define XLOG_TRACE_LOGGRANT_SIZE       2048
+#define XLOG_TRACE_ICLOG_SIZE          256
+
+void
+xlog_trace_loggrant_alloc(xlog_t *log)
+{
+       log->l_grant_trace = ktrace_alloc(XLOG_TRACE_LOGGRANT_SIZE, KM_NOFS);
+}
+
+void
+xlog_trace_loggrant_dealloc(xlog_t *log)
+{
+       ktrace_free(log->l_grant_trace);
+}
+
void
xlog_trace_loggrant(xlog_t *log, xlog_ticket_t *tic, xfs_caddr_t string)
{
        unsigned long cnts;

-       if (!log->l_grant_trace) {
-               log->l_grant_trace = ktrace_alloc(2048, KM_NOSLEEP);
-               if (!log->l_grant_trace)
-                       return;
-       }
        /* ticket counts are 1 byte each */
        cnts = ((unsigned long)tic->t_ocnt) | ((unsigned long)tic->t_cnt) << 8;

@@ -157,10 +168,20 @@ xlog_trace_loggrant(xlog_t *log, xlog_ti
}

void
+xlog_trace_iclog_alloc(xlog_in_core_t *iclog)
+{
+	iclog->ic_trace = ktrace_alloc(XLOG_TRACE_ICLOG_SIZE, KM_NOFS);
+}
+
+void
+xlog_trace_iclog_dealloc(xlog_in_core_t *iclog)
+{
+	ktrace_free(iclog->ic_trace);
+}
+
+void
xlog_trace_iclog(xlog_in_core_t *iclog, uint state)
{
-	if (!iclog->ic_trace)
-		iclog->ic_trace = ktrace_alloc(256, KM_NOFS);
	ktrace_enter(iclog->ic_trace,
		     (void *)((unsigned long)state),
		     (void *)((unsigned long)current_pid()),
@@ -170,8 +191,15 @@ xlog_trace_iclog(xlog_in_core_t *iclog, 
		     (void *)NULL, (void *)NULL);
}
#else
+
+#define	xlog_trace_loggrant_alloc(log)
+#define	xlog_trace_loggrant_dealloc(log)
#define	xlog_trace_loggrant(log,tic,string)
+
+#define	xlog_trace_iclog_alloc(iclog)
+#define	xlog_trace_iclog_dealloc(iclog)
#define	xlog_trace_iclog(iclog,state)
+
#endif /* XFS_LOG_TRACE */


@@ -1231,6 +1259,7 @@ xlog_alloc_log(xfs_mount_t    *mp,
        spin_lock_init(&log->l_grant_lock);
        sv_init(&log->l_flush_wait, 0, "flush_wait");

+       xlog_trace_loggrant_alloc(log);
        /* log record size must be multiple of BBSIZE; see xlog_rec_header_t */
        ASSERT((XFS_BUF_SIZE(bp) & BBMASK) == 0);

@@ -1285,6 +1314,8 @@ xlog_alloc_log(xfs_mount_t        *mp,
                sv_init(&iclog->ic_force_wait, SV_DEFAULT, "iclog-force");
                sv_init(&iclog->ic_write_wait, SV_DEFAULT, "iclog-write");

+               xlog_trace_iclog_alloc(iclog);
+
                iclogp = &iclog->ic_next;
        }
        *iclogp = log->l_iclog;                      /* complete ring */
@@ -1565,11 +1596,7 @@ xlog_dealloc_log(xlog_t *log)
                sv_destroy(&iclog->ic_force_wait);
                sv_destroy(&iclog->ic_write_wait);
                xfs_buf_free(iclog->ic_bp);
-#ifdef XFS_LOG_TRACE
-               if (iclog->ic_trace != NULL) {
-                       ktrace_free(iclog->ic_trace);
-               }
-#endif
+               xlog_trace_iclog_dealloc(iclog);
                next_iclog = iclog->ic_next;
                kmem_free(iclog);
                iclog = next_iclog;
@@ -1578,14 +1605,7 @@ xlog_dealloc_log(xlog_t *log)
        spinlock_destroy(&log->l_grant_lock);

        xfs_buf_free(log->l_xbuf);
-#ifdef XFS_LOG_TRACE
-       if (log->l_trace != NULL) {
-               ktrace_free(log->l_trace);
-       }
-       if (log->l_grant_trace != NULL) {
-               ktrace_free(log->l_grant_trace);
-       }
-#endif
+       xlog_trace_loggrant_dealloc(log);
        log->l_mp->m_log = NULL;
        kmem_free(log);
}       /* xlog_dealloc_log */
Index: 2.6.x-clean/fs/xfs/xfs_log_priv.h
===================================================================
--- 2.6.x-clean.orig/fs/xfs/xfs_log_priv.h
+++ 2.6.x-clean/fs/xfs/xfs_log_priv.h
@@ -448,7 +448,6 @@ typedef struct log {
        int                     l_grant_write_bytes;

#ifdef XFS_LOG_TRACE
-       struct ktrace           *l_trace;
        struct ktrace           *l_grant_trace;
#endif

Index: 2.6.x-clean/fs/xfs/xfsidbg.c
===================================================================
--- 2.6.x-clean.orig/fs/xfs/xfsidbg.c
+++ 2.6.x-clean/fs/xfs/xfsidbg.c
@@ -5864,7 +5864,7 @@ xfsidbg_xlog(xlog_t *log)
                (int)BTOBBT(log->l_grant_write_bytes),
                log->l_grant_write_bytes % BBSIZE);
#ifdef XFS_LOG_TRACE
-       qprintf("trace: 0x%p  grant_trace: use xlog value\n", log->l_trace);
+       qprintf("grant_trace: use xlog value\n");
#endif
}       /* xfsidbg_xlog */