Add a pair of helper functions to manage access to a cookie, pinning the
cache object in place for the duration to prevent cache withdrawal from
removing it:
bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
void fscache_end_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
The first is intended for internal use only, but the second will be used by
the cache backend also.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---
fs/fscache/cookie.c | 60 ++++++++++++++++++++++++++++++++++++++++
fs/fscache/internal.h | 3 ++
fs/fscache/main.c | 1 +
include/linux/fscache-cache.h | 2 +
include/trace/events/fscache.h | 29 +++++++++++++++++++
5 files changed, 95 insertions(+)
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 87ee8b666765..9b6ddbc01825 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -57,6 +57,66 @@ static void fscache_free_cookie(struct fscache_cookie *cookie)
kmem_cache_free(fscache_cookie_jar, cookie);
}
+static void __fscache_end_cookie_access(struct fscache_cookie *cookie)
+{
+ if (test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags))
+ fscache_set_cookie_stage(cookie, FSCACHE_COOKIE_STAGE_RELINQUISHING);
+ else if (test_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags))
+ fscache_set_cookie_stage(cookie, FSCACHE_COOKIE_STAGE_WITHDRAWING);
+ // PLACEHOLDER: Schedule cookie cleanup
+}
+
+/*
+ * Mark the end of an access on a cookie. This brings a deferred
+ * relinquishment or withdrawal stage into effect.
+ */
+void fscache_end_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ smp_mb__before_atomic();
+ n_accesses = atomic_dec_return(&cookie->n_accesses);
+ trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
+ n_accesses, why);
+ if (n_accesses == 0)
+ __fscache_end_cookie_access(cookie);
+}
+EXPORT_SYMBOL(fscache_end_cookie_access);
+
+/*
+ * Pin the cache behind a cookie so that we can access it.
+ */
+static void __fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ n_accesses = atomic_inc_return(&cookie->n_accesses);
+ smp_mb__after_atomic(); /* (Future) read stage after is-caching.
+ * Reread n_accesses after is-caching
+ */
+ trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
+ n_accesses, why);
+}
+
+/*
+ * Pin the cache behind a cookie so that we can access it.
+ */
+bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
+ return false;
+ __fscache_begin_cookie_access(cookie, why);
+ if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags) ||
+ !fscache_cache_is_live(cookie->volume->cache)) {
+ fscache_end_cookie_access(cookie, fscache_access_unlive);
+ return false;
+ }
+ return true;
+}
+
static inline void wake_up_cookie_stage(struct fscache_cookie *cookie)
{
/* Use a barrier to ensure that waiters see the stage variable
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 18f9a408a4f4..5669ba4bc8a9 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -34,6 +34,9 @@ extern struct kmem_cache *fscache_cookie_jar;
extern const struct seq_operations fscache_cookies_seq_ops;
extern void fscache_print_cookie(struct fscache_cookie *cookie, char prefix);
+extern bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why);
+
static inline void fscache_see_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where)
{
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 6a024c45eb0b..01d57433702c 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -23,6 +23,7 @@ MODULE_PARM_DESC(fscache_debug,
EXPORT_TRACEPOINT_SYMBOL(fscache_access_cache);
EXPORT_TRACEPOINT_SYMBOL(fscache_access_volume);
+EXPORT_TRACEPOINT_SYMBOL(fscache_access);
struct workqueue_struct *fscache_wq;
EXPORT_SYMBOL(fscache_wq);
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 7db4dda74951..a10f87421438 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -84,6 +84,8 @@ extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where);
extern void fscache_put_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where);
+extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why);
extern void fscache_set_cookie_stage(struct fscache_cookie *cookie,
enum fscache_cookie_stage stage);
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index 4b35fe9cd906..132381921be9 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -269,6 +269,35 @@ TRACE_EVENT(fscache_access_volume,
__entry->n_accesses)
);
+TRACE_EVENT(fscache_access,
+ TP_PROTO(unsigned int cookie_debug_id,
+ int ref,
+ int n_accesses,
+ enum fscache_access_trace why),
+
+ TP_ARGS(cookie_debug_id, ref, n_accesses, why),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cookie )
+ __field(int, ref )
+ __field(int, n_accesses )
+ __field(enum fscache_access_trace, why )
+ ),
+
+ TP_fast_assign(
+ __entry->cookie = cookie_debug_id;
+ __entry->ref = ref;
+ __entry->n_accesses = n_accesses;
+ __entry->why = why;
+ ),
+
+ TP_printk("c=%08x %s r=%d a=%d",
+ __entry->cookie,
+ __print_symbolic(__entry->why, fscache_access_traces),
+ __entry->ref,
+ __entry->n_accesses)
+ );
+
TRACE_EVENT(fscache_acquire,
TP_PROTO(struct fscache_cookie *cookie),
