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From: David Howells <dhowells@redhat.com>
To: linux-cachefs@redhat.com
Cc: dhowells@redhat.com, Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 11/12] fscache: Fix fscache_cookie_put() to not deref after dec
Date: Mon, 21 Jun 2021 22:47:11 +0100	[thread overview]
Message-ID: <162431203107.2908479.3259582550347000088.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <162431188431.2908479.14031376932042135080.stgit@warthog.procyon.org.uk>

fscache_cookie_put() accesses the cookie it has just put inside the
tracepoint that monitors the change - but this is something it's not
allowed to do if we didn't reduce the count to zero.

Fix this by dropping most of those values from the tracepoint and grabbing
the cookie debug ID before doing the dec.

Also take the opportunity to switch over the usage and where arguments on
the tracepoint to put the reason last.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/fscache/cookie.c            |   10 ++++++----
 fs/fscache/internal.h          |    2 +-
 fs/fscache/netfs.c             |    2 +-
 include/trace/events/fscache.h |   24 +++++++-----------------
 4 files changed, 15 insertions(+), 23 deletions(-)

diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 2558814193e9..6df3732cf1b4 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -225,8 +225,8 @@ struct fscache_cookie *fscache_hash_cookie(struct fscache_cookie *candidate)
 
 collision:
 	if (test_and_set_bit(FSCACHE_COOKIE_ACQUIRED, &cursor->flags)) {
-		trace_fscache_cookie(cursor, fscache_cookie_collision,
-				     atomic_read(&cursor->usage));
+		trace_fscache_cookie(cursor->debug_id, atomic_read(&cursor->usage),
+				     fscache_cookie_collision);
 		pr_err("Duplicate cookie detected\n");
 		fscache_print_cookie(cursor, 'O');
 		fscache_print_cookie(candidate, 'N');
@@ -305,7 +305,8 @@ struct fscache_cookie *__fscache_acquire_cookie(
 
 	cookie = fscache_hash_cookie(candidate);
 	if (!cookie) {
-		trace_fscache_cookie(candidate, fscache_cookie_discard, 1);
+		trace_fscache_cookie(candidate->debug_id, 1,
+				     fscache_cookie_discard);
 		goto out;
 	}
 
@@ -866,8 +867,9 @@ void fscache_cookie_put(struct fscache_cookie *cookie,
 	_enter("%x", cookie->debug_id);
 
 	do {
+		unsigned int cookie_debug_id = cookie->debug_id;
 		usage = atomic_dec_return(&cookie->usage);
-		trace_fscache_cookie(cookie, where, usage);
+		trace_fscache_cookie(cookie_debug_id, usage, where);
 
 		if (usage > 0)
 			return;
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index a49136c63e4b..345105dbbfd1 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -291,7 +291,7 @@ static inline void fscache_cookie_get(struct fscache_cookie *cookie,
 {
 	int usage = atomic_inc_return(&cookie->usage);
 
-	trace_fscache_cookie(cookie, where, usage);
+	trace_fscache_cookie(cookie->debug_id, usage, where);
 }
 
 /*
diff --git a/fs/fscache/netfs.c b/fs/fscache/netfs.c
index cce92216fa28..d6bdb7b5e723 100644
--- a/fs/fscache/netfs.c
+++ b/fs/fscache/netfs.c
@@ -37,7 +37,7 @@ int __fscache_register_netfs(struct fscache_netfs *netfs)
 	if (!cookie)
 		goto already_registered;
 	if (cookie != candidate) {
-		trace_fscache_cookie(candidate, fscache_cookie_discard, 1);
+		trace_fscache_cookie(candidate->debug_id, 1, fscache_cookie_discard);
 		fscache_free_cookie(candidate);
 	}
 
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index 0b9e058aba4d..55b8802740fa 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -160,37 +160,27 @@ fscache_cookie_traces;
 
 
 TRACE_EVENT(fscache_cookie,
-	    TP_PROTO(struct fscache_cookie *cookie,
-		     enum fscache_cookie_trace where,
-		     int usage),
+	    TP_PROTO(unsigned int cookie_debug_id,
+		     int usage,
+		     enum fscache_cookie_trace where),
 
-	    TP_ARGS(cookie, where, usage),
+	    TP_ARGS(cookie_debug_id, usage, where),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		cookie		)
-		    __field(unsigned int,		parent		)
 		    __field(enum fscache_cookie_trace,	where		)
 		    __field(int,			usage		)
-		    __field(int,			n_children	)
-		    __field(int,			n_active	)
-		    __field(u8,				flags		)
 			     ),
 
 	    TP_fast_assign(
-		    __entry->cookie	= cookie->debug_id;
-		    __entry->parent	= cookie->parent ? cookie->parent->debug_id : 0;
+		    __entry->cookie	= cookie_debug_id;
 		    __entry->where	= where;
 		    __entry->usage	= usage;
-		    __entry->n_children	= atomic_read(&cookie->n_children);
-		    __entry->n_active	= atomic_read(&cookie->n_active);
-		    __entry->flags	= cookie->flags;
 			   ),
 
-	    TP_printk("%s c=%08x u=%d p=%08x Nc=%d Na=%d f=%02x",
+	    TP_printk("%s c=%08x u=%d",
 		      __print_symbolic(__entry->where, fscache_cookie_traces),
-		      __entry->cookie, __entry->usage,
-		      __entry->parent, __entry->n_children, __entry->n_active,
-		      __entry->flags)
+		      __entry->cookie, __entry->usage)
 	    );
 
 TRACE_EVENT(fscache_netfs,



  parent reply	other threads:[~2021-06-21 21:47 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-21 21:44 [PATCH 00/12] fscache: Some prep work for fscache rewrite David Howells
2021-06-21 21:44 ` [PATCH 01/12] fscache: Select netfs stats if fscache stats are enabled David Howells
2021-06-21 21:45 ` [PATCH 02/12] netfs: Move cookie debug ID to struct netfs_cache_resources David Howells
2021-06-21 21:45 ` [PATCH 03/12] cachefiles: Use file_inode() rather than accessing ->f_inode David Howells
2021-06-21 21:45 ` [PATCH 04/12] fscache: Add a cookie debug ID and use that in traces David Howells
2021-06-21 21:45 ` [PATCH 05/12] fscache: Procfile to display cookies David Howells
2021-06-21 21:45 ` [PATCH 06/12] fscache, cachefiles: Remove the histogram stuff David Howells
2021-06-21 21:46 ` [PATCH 07/12] fscache: Remove the object list procfile David Howells
2021-06-21 21:46 ` [PATCH 08/12] fscache: Change %p in format strings to something else David Howells
2021-06-21 21:46 ` [PATCH 09/12] cachefiles: " David Howells
2021-06-21 21:46 ` [PATCH 10/12] fscache: Fix cookie key hashing David Howells
2021-08-24 16:11   ` Jeff Layton
2021-08-25 14:04   ` David Howells
2021-06-21 21:47 ` David Howells [this message]
2021-08-24 14:24   ` [PATCH 11/12] fscache: Fix fscache_cookie_put() to not deref after dec Jeff Layton
2021-08-25 14:05   ` David Howells
2021-06-21 21:47 ` [PATCH 12/12] fscache: Use refcount_t for the cookie refcount instead of atomic_t David Howells
2021-08-24 14:25 ` [PATCH 00/12] fscache: Some prep work for fscache rewrite Jeff Layton
2021-08-27 12:31 ` [PATCH v2 04/12] fscache: Add a cookie debug ID and use that in traces David Howells
2021-08-27 12:49   ` [Linux-cachefs] " Marc Dionne

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