Add a pair of helper functions to pin/unpin a cache that we're wanting to
do a high-level access to (such as creating or removing a volume).
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---
fs/fscache/cache.c | 37 ++++++++++++++++++++++++++++++++++++
fs/fscache/internal.h | 2 ++
fs/fscache/main.c | 2 ++
include/trace/events/fscache.h | 41 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 82 insertions(+)
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
index da08e29ee5b9..3cde698c5015 100644
--- a/fs/fscache/cache.c
+++ b/fs/fscache/cache.c
@@ -171,6 +171,43 @@ void fscache_put_cache(struct fscache_cache *cache,
}
EXPORT_SYMBOL(fscache_put_cache);
+/*
+ * Get an increment on a cache's access counter if the cache is live to prevent
+ * it from going away whilst we're accessing it.
+ */
+bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ if (!fscache_cache_is_live(cache))
+ return false;
+
+ n_accesses = atomic_inc_return(&cache->n_accesses);
+ smp_mb__after_atomic(); /* Reread live flag after n_accesses */
+ trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
+ n_accesses, why);
+ if (!fscache_cache_is_live(cache)) {
+ fscache_end_cache_access(cache, fscache_access_unlive);
+ return false;
+ }
+ return true;
+}
+
+/*
+ * Drop an increment on a cache's access counter.
+ */
+void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ smp_mb__before_atomic();
+ n_accesses = atomic_dec_return(&cache->n_accesses);
+ trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
+ n_accesses, why);
+ if (n_accesses == 0)
+ wake_up_var(&cache->n_accesses);
+}
+
#ifdef CONFIG_PROC_FS
static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 9daacd7de9ea..5546c24d18d8 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -23,6 +23,8 @@
#ifdef CONFIG_PROC_FS
extern const struct seq_operations fscache_caches_seq_ops;
#endif
+bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why);
+void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why);
struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache);
/*
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index fad9c1933987..e1f14b29cff4 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -21,6 +21,8 @@ module_param_named(debug, fscache_debug, uint,
MODULE_PARM_DESC(fscache_debug,
"FS-Cache debugging mask");
+EXPORT_TRACEPOINT_SYMBOL(fscache_access_cache);
+
struct workqueue_struct *fscache_wq;
EXPORT_SYMBOL(fscache_wq);
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index cfa4c153c72b..d09d7e3ac86c 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -59,6 +59,12 @@ enum fscache_cookie_trace {
fscache_cookie_see_work,
};
+enum fscache_access_trace {
+ fscache_access_cache_pin,
+ fscache_access_cache_unpin,
+ fscache_access_unlive,
+};
+
#endif
/*
@@ -101,6 +107,11 @@ enum fscache_cookie_trace {
EM(fscache_cookie_see_withdraw, "- x-wth") \
E_(fscache_cookie_see_work, "- work ")
+#define fscache_access_traces \
+ EM(fscache_access_cache_pin, "PIN cache ") \
+ EM(fscache_access_cache_unpin, "UNPIN cache ") \
+ E_(fscache_access_unlive, "END unlive ")
+
/*
* Export enum symbols via userspace.
*/
@@ -112,6 +123,7 @@ enum fscache_cookie_trace {
fscache_cache_traces;
fscache_volume_traces;
fscache_cookie_traces;
+fscache_access_traces;
/*
* Now redefine the EM() and E_() macros to map the enums to the strings that
@@ -198,6 +210,35 @@ TRACE_EVENT(fscache_cookie,
__entry->ref)
);
+TRACE_EVENT(fscache_access_cache,
+ TP_PROTO(unsigned int cache_debug_id,
+ int ref,
+ int n_accesses,
+ enum fscache_access_trace why),
+
+ TP_ARGS(cache_debug_id, ref, n_accesses, why),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cache )
+ __field(int, ref )
+ __field(int, n_accesses )
+ __field(enum fscache_access_trace, why )
+ ),
+
+ TP_fast_assign(
+ __entry->cache = cache_debug_id;
+ __entry->ref = ref;
+ __entry->n_accesses = n_accesses;
+ __entry->why = why;
+ ),
+
+ TP_printk("C=%08x %s r=%d a=%d",
+ __entry->cache,
+ __print_symbolic(__entry->why, fscache_access_traces),
+ __entry->ref,
+ __entry->n_accesses)
+ );
+
TRACE_EVENT(fscache_acquire,
TP_PROTO(struct fscache_cookie *cookie),
