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-rw-r--r--fs/jffs2/README.Locking21
1 files changed, 21 insertions, 0 deletions
diff --git a/fs/jffs2/README.Locking b/fs/jffs2/README.Locking
index b7943439b6ec..c8f0bd64e53e 100644
--- a/fs/jffs2/README.Locking
+++ b/fs/jffs2/README.Locking
@@ -150,3 +150,24 @@ the buffer.
150 150
151Ordering constraints: 151Ordering constraints:
152 Lock wbuf_sem last, after the alloc_sem or and f->sem. 152 Lock wbuf_sem last, after the alloc_sem or and f->sem.
153
154
155 c->xattr_sem
156 ------------
157
158This read/write semaphore protects against concurrent access to the
159xattr related objects which include stuff in superblock and ic->xref.
160In read-only path, write-semaphore is too much exclusion. It's enough
161by read-semaphore. But you must hold write-semaphore when updating,
162creating or deleting any xattr related object.
163
164Once xattr_sem released, there would be no assurance for the existence
165of those objects. Thus, a series of processes is often required to retry,
166when updating such a object is necessary under holding read semaphore.
167For example, do_jffs2_getxattr() holds read-semaphore to scan xref and
168xdatum at first. But it retries this process with holding write-semaphore
169after release read-semaphore, if it's necessary to load name/value pair
170from medium.
171
172Ordering constraints:
173 Lock xattr_sem last, after the alloc_sem.