Add a pair of helper functions to manage access to a volume, pinning the
volume in place for the duration to prevent cache withdrawal from removing
it:
bool fscache_begin_volume_access(struct fscache_volume *volume,
enum fscache_access_trace why);
void fscache_end_volume_access(struct fscache_volume *volume,
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/internal.h | 2 ++
fs/fscache/main.c | 1 +
fs/fscache/volume.c | 47 ++++++++++++++++++++++++++++++++++++++++
include/linux/fscache-cache.h | 3 +++
include/trace/events/fscache.h | 30 ++++++++++++++++++++++++++
5 files changed, 83 insertions(+)
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 5546c24d18d8..18f9a408a4f4 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -107,6 +107,8 @@ struct fscache_volume *fscache_get_volume(struct fscache_volume *volume,
enum fscache_volume_trace where);
void fscache_put_volume(struct fscache_volume *volume,
enum fscache_volume_trace where);
+bool fscache_begin_volume_access(struct fscache_volume *volume,
+ enum fscache_access_trace why);
void fscache_create_volume(struct fscache_volume *volume, bool wait);
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index e1f14b29cff4..6a024c45eb0b 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -22,6 +22,7 @@ MODULE_PARM_DESC(fscache_debug,
"FS-Cache debugging mask");
EXPORT_TRACEPOINT_SYMBOL(fscache_access_cache);
+EXPORT_TRACEPOINT_SYMBOL(fscache_access_volume);
struct workqueue_struct *fscache_wq;
EXPORT_SYMBOL(fscache_wq);
diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c
index 924851888f18..d539d6ec2664 100644
--- a/fs/fscache/volume.c
+++ b/fs/fscache/volume.c
@@ -33,6 +33,53 @@ static void fscache_see_volume(struct fscache_volume *volume,
trace_fscache_volume(volume->debug_id, ref, where);
}
+/*
+ * Pin the cache behind a volume so that we can access it.
+ */
+static void __fscache_begin_volume_access(struct fscache_volume *volume,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ n_accesses = atomic_inc_return(&volume->n_accesses);
+ smp_mb__after_atomic();
+ trace_fscache_access_volume(volume->debug_id, refcount_read(&volume->ref),
+ n_accesses, why);
+}
+
+/*
+ * If the cache behind a volume is live, pin it so that we can access it.
+ */
+bool fscache_begin_volume_access(struct fscache_volume *volume,
+ enum fscache_access_trace why)
+{
+ if (!fscache_cache_is_live(volume->cache))
+ return false;
+ __fscache_begin_volume_access(volume, why);
+ if (!fscache_cache_is_live(volume->cache)) {
+ fscache_end_volume_access(volume, fscache_access_unlive);
+ return false;
+ }
+ return true;
+}
+
+/*
+ * Mark the end of an access on a volume.
+ */
+void fscache_end_volume_access(struct fscache_volume *volume,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ smp_mb__before_atomic();
+ n_accesses = atomic_dec_return(&volume->n_accesses);
+ trace_fscache_access_volume(volume->debug_id, refcount_read(&volume->ref),
+ n_accesses, why);
+ if (n_accesses == 0)
+ wake_up_var(&volume->n_accesses);
+}
+EXPORT_SYMBOL(fscache_end_volume_access);
+
static long fscache_compare_volume(const struct fscache_volume *a,
const struct fscache_volume *b)
{
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index e075cca1a30d..7db4dda74951 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -77,6 +77,9 @@ extern struct fscache_cache *fscache_acquire_cache(const char *name);
extern void fscache_put_cache(struct fscache_cache *cache,
enum fscache_cache_trace where);
+extern void fscache_end_volume_access(struct fscache_volume *volume,
+ enum fscache_access_trace why);
+
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,
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index d09d7e3ac86c..4b35fe9cd906 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -40,6 +40,7 @@ enum fscache_volume_trace {
fscache_volume_put_relinquish,
fscache_volume_see_create_work,
fscache_volume_see_hash_wake,
+ fscache_volume_wait_create_work,
};
enum fscache_cookie_trace {
@@ -239,6 +240,35 @@ TRACE_EVENT(fscache_access_cache,
__entry->n_accesses)
);
+TRACE_EVENT(fscache_access_volume,
+ TP_PROTO(unsigned int volume_debug_id,
+ int ref,
+ int n_accesses,
+ enum fscache_access_trace why),
+
+ TP_ARGS(volume_debug_id, ref, n_accesses, why),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, volume )
+ __field(int, ref )
+ __field(int, n_accesses )
+ __field(enum fscache_access_trace, why )
+ ),
+
+ TP_fast_assign(
+ __entry->volume = volume_debug_id;
+ __entry->ref = ref;
+ __entry->n_accesses = n_accesses;
+ __entry->why = why;
+ ),
+
+ TP_printk("V=%08x %s r=%d a=%d",
+ __entry->volume,
+ __print_symbolic(__entry->why, fscache_access_traces),
+ __entry->ref,
+ __entry->n_accesses)
+ );
+
TRACE_EVENT(fscache_acquire,
TP_PROTO(struct fscache_cookie *cookie),
