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simplify lookup_open()/atomic_open() - do the temporary mnt_want_write() early
The write ref to vfsmount taken in lookup_open()/atomic_open() is going to be dropped; we take the one to stay in dentry_open(). Just grab the temporary in caller if it looks like we are going to need it (create/truncate/writable open) and pass (by value) "has it succeeded" flag. Instead of doing mnt_want_write() inside, check that flag and treat "false" as "mnt_want_write() has just failed". mnt_want_write() is cheap and the things get considerably simpler and more robust that way - we get it and drop it in the same function, to start with, rather than passing a "has something in the guts of really scary functions taken it" back to caller. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
parent
f8310c5920
commit
64894cf843
51
fs/namei.c
51
fs/namei.c
@ -2395,7 +2395,7 @@ static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode)
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static int atomic_open(struct nameidata *nd, struct dentry *dentry,
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struct path *path, struct file *file,
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const struct open_flags *op,
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bool *want_write, bool need_lookup,
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bool got_write, bool need_lookup,
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int *opened)
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{
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struct inode *dir = nd->path.dentry->d_inode;
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@ -2432,12 +2432,9 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
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* Another problem is returing the "right" error value (e.g. for an
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* O_EXCL open we want to return EEXIST not EROFS).
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*/
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if ((open_flag & (O_CREAT | O_TRUNC)) ||
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(open_flag & O_ACCMODE) != O_RDONLY) {
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error = mnt_want_write(nd->path.mnt);
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if (!error) {
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*want_write = true;
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} else if (!(open_flag & O_CREAT)) {
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if (((open_flag & (O_CREAT | O_TRUNC)) ||
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(open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) {
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if (!(open_flag & O_CREAT)) {
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/*
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* No O_CREATE -> atomicity not a requirement -> fall
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* back to lookup + open
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@ -2445,11 +2442,11 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
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goto no_open;
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} else if (open_flag & (O_EXCL | O_TRUNC)) {
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/* Fall back and fail with the right error */
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create_error = error;
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create_error = -EROFS;
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goto no_open;
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} else {
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/* No side effects, safe to clear O_CREAT */
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create_error = error;
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create_error = -EROFS;
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open_flag &= ~O_CREAT;
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}
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}
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@ -2556,7 +2553,7 @@ looked_up:
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static int lookup_open(struct nameidata *nd, struct path *path,
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struct file *file,
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const struct open_flags *op,
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bool *want_write, int *opened)
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bool got_write, int *opened)
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{
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struct dentry *dir = nd->path.dentry;
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struct inode *dir_inode = dir->d_inode;
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@ -2574,7 +2571,7 @@ static int lookup_open(struct nameidata *nd, struct path *path,
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goto out_no_open;
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if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {
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return atomic_open(nd, dentry, path, file, op, want_write,
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return atomic_open(nd, dentry, path, file, op, got_write,
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need_lookup, opened);
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}
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@ -2598,10 +2595,10 @@ static int lookup_open(struct nameidata *nd, struct path *path,
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* a permanent write count is taken through
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* the 'struct file' in finish_open().
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*/
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error = mnt_want_write(nd->path.mnt);
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if (error)
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if (!got_write) {
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error = -EROFS;
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goto out_dput;
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*want_write = true;
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}
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*opened |= FILE_CREATED;
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error = security_path_mknod(&nd->path, dentry, mode, 0);
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if (error)
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@ -2631,7 +2628,7 @@ static int do_last(struct nameidata *nd, struct path *path,
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struct dentry *dir = nd->path.dentry;
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int open_flag = op->open_flag;
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bool will_truncate = (open_flag & O_TRUNC) != 0;
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bool want_write = false;
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bool got_write = false;
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int acc_mode = op->acc_mode;
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struct inode *inode;
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bool symlink_ok = false;
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@ -2700,8 +2697,18 @@ static int do_last(struct nameidata *nd, struct path *path,
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}
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retry_lookup:
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if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
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error = mnt_want_write(nd->path.mnt);
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if (!error)
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got_write = true;
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/*
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* do _not_ fail yet - we might not need that or fail with
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* a different error; let lookup_open() decide; we'll be
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* dropping this one anyway.
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*/
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}
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mutex_lock(&dir->d_inode->i_mutex);
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error = lookup_open(nd, path, file, op, &want_write, opened);
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error = lookup_open(nd, path, file, op, got_write, opened);
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mutex_unlock(&dir->d_inode->i_mutex);
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if (error <= 0) {
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@ -2736,9 +2743,9 @@ retry_lookup:
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* possible mount and symlink following (this might be optimized away if
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* necessary...)
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*/
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if (want_write) {
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if (got_write) {
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mnt_drop_write(nd->path.mnt);
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want_write = false;
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got_write = false;
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}
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error = -EEXIST;
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@ -2803,7 +2810,7 @@ finish_open:
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error = mnt_want_write(nd->path.mnt);
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if (error)
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goto out;
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want_write = true;
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got_write = true;
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}
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finish_open_created:
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error = may_open(&nd->path, acc_mode, open_flag);
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@ -2830,7 +2837,7 @@ opened:
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goto exit_fput;
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}
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out:
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if (want_write)
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if (got_write)
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mnt_drop_write(nd->path.mnt);
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path_put(&save_parent);
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terminate_walk(nd);
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@ -2854,9 +2861,9 @@ stale_open:
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nd->inode = dir->d_inode;
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save_parent.mnt = NULL;
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save_parent.dentry = NULL;
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if (want_write) {
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if (got_write) {
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mnt_drop_write(nd->path.mnt);
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want_write = false;
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got_write = false;
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}
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retried = true;
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goto retry_lookup;
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