This is a note to let you know that I've just added the patch titled
Nest rename_lock inside vfsmount_lock
to the 3.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nest-rename_lock-inside-vfsmount_lock.patch
and it can be found in the queue-3.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Tue, 26 Mar 2013 18:25:57 -0400
Subject: Nest rename_lock inside vfsmount_lock
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a upstream.
... lest we get livelocks between path_is_under() and d_path() and friends.
The thing is, wrt fairness lglocks are more similar to rwsems than to rwlocks;
it is possible to have thread B spin on attempt to take lock shared while thread
A is already holding it shared, if B is on lower-numbered CPU than A and there's
a thread C spinning on attempt to take the same lock exclusive.
As the result, we need consistent ordering between vfsmount_lock (lglock) and
rename_lock (seq_lock), even though everything that takes both is going to take
vfsmount_lock only shared.
Spotted-by: Brad Spengler <spender@xxxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/dcache.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2552,7 +2552,6 @@ static int prepend_path(const struct pat
bool slash = false;
int error = 0;
- br_read_lock(&vfsmount_lock);
while (dentry != root->dentry || vfsmnt != root->mnt) {
struct dentry * parent;
@@ -2582,8 +2581,6 @@ static int prepend_path(const struct pat
if (!error && !slash)
error = prepend(buffer, buflen, "/", 1);
-out:
- br_read_unlock(&vfsmount_lock);
return error;
global_root:
@@ -2600,7 +2597,7 @@ global_root:
error = prepend(buffer, buflen, "/", 1);
if (!error)
error = is_mounted(vfsmnt) ? 1 : 2;
- goto out;
+ return error;
}
/**
@@ -2627,9 +2624,11 @@ char *__d_path(const struct path *path,
int error;
prepend(&res, &buflen, "\0", 1);
+ br_read_lock(&vfsmount_lock);
write_seqlock(&rename_lock);
error = prepend_path(path, root, &res, &buflen);
write_sequnlock(&rename_lock);
+ br_read_unlock(&vfsmount_lock);
if (error < 0)
return ERR_PTR(error);
@@ -2646,9 +2645,11 @@ char *d_absolute_path(const struct path
int error;
prepend(&res, &buflen, "\0", 1);
+ br_read_lock(&vfsmount_lock);
write_seqlock(&rename_lock);
error = prepend_path(path, &root, &res, &buflen);
write_sequnlock(&rename_lock);
+ br_read_unlock(&vfsmount_lock);
if (error > 1)
error = -EINVAL;
@@ -2712,11 +2713,13 @@ char *d_path(const struct path *path, ch
return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
get_fs_root(current->fs, &root);
+ br_read_lock(&vfsmount_lock);
write_seqlock(&rename_lock);
error = path_with_deleted(path, &root, &res, &buflen);
+ write_sequnlock(&rename_lock);
+ br_read_unlock(&vfsmount_lock);
if (error < 0)
res = ERR_PTR(error);
- write_sequnlock(&rename_lock);
path_put(&root);
return res;
}
@@ -2871,6 +2874,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
get_fs_root_and_pwd(current->fs, &root, &pwd);
error = -ENOENT;
+ br_read_lock(&vfsmount_lock);
write_seqlock(&rename_lock);
if (!d_unlinked(pwd.dentry)) {
unsigned long len;
@@ -2880,6 +2884,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
prepend(&cwd, &buflen, "\0", 1);
error = prepend_path(&pwd, &root, &cwd, &buflen);
write_sequnlock(&rename_lock);
+ br_read_unlock(&vfsmount_lock);
if (error < 0)
goto out;
@@ -2900,6 +2905,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
}
} else {
write_sequnlock(&rename_lock);
+ br_read_unlock(&vfsmount_lock);
}
out:
Patches currently in stable-queue which might be from viro@xxxxxxxxxxxxxxxxxx are
queue-3.8/nest-rename_lock-inside-vfsmount_lock.patch
queue-3.8/vt-synchronize_rcu-under-spinlock-is-not-nice.patch
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