Commit-ID: 7088efa9137a15d7d21e3abce73e40c9c8a18d68 Gitweb: https://git.kernel.org/tip/7088efa9137a15d7d21e3abce73e40c9c8a18d68 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Mon, 9 Oct 2017 10:04:27 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Mon, 4 Dec 2017 10:52:52 -0800 fs/dcache: Use release-acquire for name/length update The code in __d_alloc() carefully orders filling in the NUL character of the name (and the length, hash, and the name itself) with assigning of the name itself. However, prepend_name() does not order the accesses to the ->name and ->len fields, other than on TSO systems. This commit therefore replaces prepend_name()'s READ_ONCE() of ->name with an smp_load_acquire(), which orders against the subsequent READ_ONCE() of ->len. Because READ_ONCE() now incorporates smp_read_barrier_depends(), prepend_name()'s smp_read_barrier_depends() is removed. Finally, to save a line, the smp_wmb()/store pair in __d_alloc() is replaced by smp_store_release(). Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: <linux-fsdevel@xxxxxxxxxxxxxxx> --- fs/dcache.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 5c7df1d..379dce8 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1636,8 +1636,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) dname[name->len] = 0; /* Make sure we always see the terminating NUL character */ - smp_wmb(); - dentry->d_name.name = dname; + smp_store_release(&dentry->d_name.name, dname); /* ^^^ */ dentry->d_lockref.count = 1; dentry->d_flags = 0; @@ -3047,17 +3046,14 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen) * retry it again when a d_move() does happen. So any garbage in the buffer * due to mismatched pointer and length will be discarded. * - * Data dependency barrier is needed to make sure that we see that terminating - * NUL. Alpha strikes again, film at 11... + * Load acquire is needed to make sure that we see that terminating NUL. */ static int prepend_name(char **buffer, int *buflen, const struct qstr *name) { - const char *dname = READ_ONCE(name->name); + const char *dname = smp_load_acquire(&name->name); /* ^^^ */ u32 dlen = READ_ONCE(name->len); char *p; - smp_read_barrier_depends(); - *buflen -= dlen + 1; if (*buflen < 0) return -ENAMETOOLONG;
