xiaomi-sm8450/android_kernel_xiaomi_sm8450
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New locking/refcounting for fs_struct

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* 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>
This commit is contained in:
Al Viro
2009-03-30 07:20:30 -04:00
parent 3e93cd6718
commit 498052bba5
7 changed files with 121 additions and 44 deletions
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37
kernel/fork.c
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@@ -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: