pnfs/flexfiles: protect ktime manipulation with mirror lock

It looks as if xchg() and cmpxchg() are not available for 64-bit integers on sparc32:

> New breakage seen in linux-next today:
>
> ERROR: "__xchg_called_with_bad_pointer" [fs/nfs/flexfilelayout/nfs_layout_flexfiles.ko] undefined!
> ERROR: "__cmpxchg_called_with_bad_pointer" [fs/nfs/flexfilelayout/nfs_layout_flexfiles.ko] undefined!
> make[2]: *** [__modpost] Error 1
> make[1]: *** [modules] Error 2

Given that mirror ktime manipulation is already under mirror->lock, let's make use of the fact.

Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index d3b3b623671143b73ee64616d807448d95759715..85b4234b80906efd6a872827531f13c788dee6a8 100644 (file)
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -417,21 +417,9 @@ ff_layout_get_lseg_count(struct nfs4_ff_layout_segment *fls)
 static void
 nfs4_ff_start_busy_timer(struct nfs4_ff_busy_timer *timer)
 {
-       ktime_t old, new;
-
-       /*
-        * Note: careful here!
-        * If the counter is zero, then we must not increment it until after
-        * we've set the start_time.
-        * If we were instead to use atomic_inc_return(), then another
-        * request might come in, bump, and then call end_busy_timer()
-        * before we've set the timer->start_time.
-        */
-       old = timer->start_time;
-       if (atomic_inc_not_zero(&timer->n_ops) == 0) {
-               new = ktime_get();
-               cmpxchg(&timer->start_time.tv64, old.tv64, new.tv64);
-               atomic_inc(&timer->n_ops);
+       /* first IO request? */
+       if (atomic_inc_return(&timer->n_ops) == 1) {
+               timer->start_time = ktime_get();
        }
 }
 
@@ -440,9 +428,12 @@ nfs4_ff_end_busy_timer(struct nfs4_ff_busy_timer *timer)
 {
        ktime_t start, now;
 
+       if (atomic_dec_return(&timer->n_ops) < 0)
+               WARN_ON_ONCE(1);
+
        now = ktime_get();
-       start.tv64 = xchg(&timer->start_time.tv64, now.tv64);
-       atomic_dec(&timer->n_ops);
+       start = timer->start_time;
+       timer->start_time = now;
        return ktime_sub(now, start);
 }
 
@@ -460,8 +451,10 @@ nfs4_ff_layoutstat_start_io(struct nfs4_ff_layout_mirror *mirror,
        ktime_t now = ktime_get();
 
        nfs4_ff_start_busy_timer(&layoutstat->busy_timer);
-       cmpxchg(&mirror->start_time.tv64, notime.tv64, now.tv64);
-       cmpxchg(&mirror->last_report_time.tv64, notime.tv64, now.tv64);
+       if (ktime_equal(mirror->start_time, notime))
+               mirror->start_time = now;
+       if (ktime_equal(mirror->last_report_time, notime))
+               mirror->last_report_time = now;
        if (ktime_to_ms(ktime_sub(now, mirror->last_report_time)) >=
                        FF_LAYOUTSTATS_REPORT_INTERVAL) {
                mirror->last_report_time = now;