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authorAl Viro <viro@zeniv.linux.org.uk>2009-03-30 07:20:30 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2009-03-31 23:00:26 -0400
commit498052bba55ecaff58db6a1436b0e25bfd75a7ff (patch)
treebd3644ac60737e3733995a203acebd70cfd1b21b /kernel/fork.c
parent3e93cd671813e204c258f1e6c797959920cf7772 (diff)
downloadlwn-498052bba55ecaff58db6a1436b0e25bfd75a7ff.tar.gz
lwn-498052bba55ecaff58db6a1436b0e25bfd75a7ff.zip
New locking/refcounting for fs_struct
* all changes of current->fs are done under task_lock and write_lock of old fs->lock * refcount is not atomic anymore (same protection) * its decrements are done when removing reference from current; at the same time we decide whether to free it. * put_fs_struct() is gone * new field - ->in_exec. Set by check_unsafe_exec() if we are trying to do execve() and only subthreads share fs_struct. Cleared when finishing exec (success and failure alike). Makes CLONE_FS fail with -EAGAIN if set. * check_unsafe_exec() may fail with -EAGAIN if another execve() from subthread is in progress. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c37
1 files changed, 27 insertions, 10 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 05c02dc586b1..51f138a131de 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -683,11 +683,19 @@ fail_nomem:
static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
{
+ struct fs_struct *fs = current->fs;
if (clone_flags & CLONE_FS) {
- atomic_inc(&current->fs->count);
+ /* tsk->fs is already what we want */
+ write_lock(&fs->lock);
+ if (fs->in_exec) {
+ write_unlock(&fs->lock);
+ return -EAGAIN;
+ }
+ fs->users++;
+ write_unlock(&fs->lock);
return 0;
}
- tsk->fs = copy_fs_struct(current->fs);
+ tsk->fs = copy_fs_struct(fs);
if (!tsk->fs)
return -ENOMEM;
return 0;
@@ -1518,12 +1526,16 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
{
struct fs_struct *fs = current->fs;
- if ((unshare_flags & CLONE_FS) &&
- (fs && atomic_read(&fs->count) > 1)) {
- *new_fsp = copy_fs_struct(current->fs);
- if (!*new_fsp)
- return -ENOMEM;
- }
+ if (!(unshare_flags & CLONE_FS) || !fs)
+ return 0;
+
+ /* don't need lock here; in the worst case we'll do useless copy */
+ if (fs->users == 1)
+ return 0;
+
+ *new_fsp = copy_fs_struct(fs);
+ if (!*new_fsp)
+ return -ENOMEM;
return 0;
}
@@ -1639,8 +1651,13 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
if (new_fs) {
fs = current->fs;
+ write_lock(&fs->lock);
current->fs = new_fs;
- new_fs = fs;
+ if (--fs->users)
+ new_fs = NULL;
+ else
+ new_fs = fs;
+ write_unlock(&fs->lock);
}
if (new_mm) {
@@ -1679,7 +1696,7 @@ bad_unshare_cleanup_sigh:
bad_unshare_cleanup_fs:
if (new_fs)
- put_fs_struct(new_fs);
+ free_fs_struct(new_fs);
bad_unshare_cleanup_thread:
bad_unshare_out: