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Subject[RFC PATCH 5/6] mm: Add locking to msharefs syscalls
Date
Lock the root inode for msharefs when creating a new file or deleting
an existing one to avoid races. mshare syscalls are low frequency
operations, so locking the root inode is reasonable.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
mm/mshare.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index 8273136363cc..adfd5a280e5b 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -194,11 +194,12 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
err = msharefs_d_hash(msharefs_sb->s_root, &namestr);
if (err)
goto err_out;
+ inode_lock(d_inode(msharefs_sb->s_root));
dentry = d_lookup(msharefs_sb->s_root, &namestr);
if (dentry && (oflag & (O_EXCL|O_CREAT))) {
err = -EEXIST;
dput(dentry);
- goto err_out;
+ goto err_unlock_inode;
}

if (dentry) {
@@ -231,6 +232,7 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
goto err_relinfo;
}

+ inode_unlock(d_inode(msharefs_sb->s_root));
putname(fname);
return 0;

@@ -238,6 +240,8 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
kfree(info);
err_relmm:
mmput(mm);
+err_unlock_inode:
+ inode_unlock(d_inode(msharefs_sb->s_root));
err_out:
putname(fname);
return err;
@@ -263,10 +267,11 @@ SYSCALL_DEFINE1(mshare_unlink, const char *, name)
err = msharefs_d_hash(msharefs_sb->s_root, &namestr);
if (err)
goto err_out;
+ inode_lock(d_inode(msharefs_sb->s_root));
dentry = d_lookup(msharefs_sb->s_root, &namestr);
if (dentry == NULL) {
err = -EINVAL;
- goto err_out;
+ goto err_unlock_inode;
}

inode = d_inode(dentry);
@@ -289,11 +294,14 @@ SYSCALL_DEFINE1(mshare_unlink, const char *, name)
dput(dentry);
}

+ inode_unlock(d_inode(msharefs_sb->s_root));
putname(fname);
return 0;

err_dput:
dput(dentry);
+err_unlock_inode:
+ inode_unlock(d_inode(msharefs_sb->s_root));
err_out:
putname(fname);
return err;
--
2.32.0
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