Quoting Matt Helsley ([email protected]):
> This patch avoids holding the mmap semaphore while walking VMAs in response to
> programs which read or follow the /proc/<pid|self>/exe symlink. This also allows us
> to merge mmu and nommu proc_exe_link() functions. The costs are holding a separate
> reference to the executable file stored in the task struct and increased code in
> fork, exec, and exit paths.
>
> Signed-off-by: Matt Helsley <[email protected]>
> ---
>
> Compiled and passed simple tests for regressions when patched against a 2.6.20
> and 2.6.22-rc2-mm1 kernel.
>
> fs/exec.c | 5 +++--
> fs/proc/base.c | 20 ++++++++++++++++++++
> fs/proc/internal.h | 1 -
> fs/proc/task_mmu.c | 34 ----------------------------------
> fs/proc/task_nommu.c | 34 ----------------------------------
> include/linux/sched.h | 1 +
> kernel/exit.c | 2 ++
> kernel/fork.c | 10 +++++++++-
> 8 files changed, 35 insertions(+), 72 deletions(-)
>
> Index: linux-2.6.22-rc2-mm1/include/linux/sched.h
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/include/linux/sched.h
> +++ linux-2.6.22-rc2-mm1/include/linux/sched.h
> @@ -988,10 +988,11 @@ struct task_struct {
> int oomkilladj; /* OOM kill score adjustment (bit shift). */
> char comm[TASK_COMM_LEN]; /* executable name excluding path
> - access with [gs]et_task_comm (which lock
> it with task_lock())
> - initialized normally by flush_old_exec */
> + struct file *exe_file;
> /* file system info */
> int link_count, total_link_count;
> #ifdef CONFIG_SYSVIPC
> /* ipc stuff */
> struct sysv_sem sysvsem;
> Index: linux-2.6.22-rc2-mm1/fs/exec.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/fs/exec.c
> +++ linux-2.6.22-rc2-mm1/fs/exec.c
> @@ -1106,12 +1106,13 @@ int search_binary_handler(struct linux_b
> read_unlock(&binfmt_lock);
> retval = fn(bprm, regs);
> if (retval >= 0) {
> put_binfmt(fmt);
> allow_write_access(bprm->file);
> - if (bprm->file)
> - fput(bprm->file);
> + if (current->exe_file)
> + fput(current->exe_file);
> + current->exe_file = bprm->file;
> bprm->file = NULL;
> current->did_exec = 1;
> proc_exec_connector(current);
> return retval;
> }
> Index: linux-2.6.22-rc2-mm1/fs/proc/base.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/fs/proc/base.c
> +++ linux-2.6.22-rc2-mm1/fs/proc/base.c
> @@ -951,10 +951,30 @@ const struct file_operations proc_pid_sc
> .write = sched_write,
> .llseek = seq_lseek,
> .release = seq_release,
> };
>
> +static int proc_exe_link(struct inode *inode, struct dentry **dentry,
> + struct vfsmount **mnt)
> +{
> + int error;
> + struct task_struct *task;
> +
> + task = get_proc_task(inode);
> + if (!task)
> + return -ENOENT;
> + error = -ENOSYS;
> + if (!task->exe_file)
> + goto out;
> + *mnt = mntget(task->exe_file->f_path.mnt);
> + *dentry = dget(task->exe_file->f_path.dentry);
> + error = 0;
> +out:
> + put_task_struct(task);
> + return error;
> +}
> +
> static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
> {
> struct inode *inode = dentry->d_inode;
> int error = -EACCES;
>
> Index: linux-2.6.22-rc2-mm1/kernel/exit.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/kernel/exit.c
> +++ linux-2.6.22-rc2-mm1/kernel/exit.c
> @@ -924,10 +924,12 @@ fastcall void do_exit(long code)
> if (unlikely(tsk->audit_context))
> audit_free(tsk);
>
> taskstats_exit(tsk, group_dead);
>
> + if (tsk->exe_file)
> + fput(tsk->exe_file);
Hi,
just taking a cursory look so I may be missing something, but doesn't
this leave the possibility that right here, with tsk->exe_file being
put, another task would try to look at tsk's /proc/tsk->pid/exe?
thanks,
-serge
> exit_mm(tsk);
>
> if (group_dead)
> acct_process();
> exit_sem(tsk);
> Index: linux-2.6.22-rc2-mm1/kernel/fork.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/kernel/fork.c
> +++ linux-2.6.22-rc2-mm1/kernel/fork.c
> @@ -1163,10 +1163,13 @@ static struct task_struct *copy_process(
>
> /* ok, now we should be set up.. */
> p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
> p->pdeath_signal = 0;
> p->exit_state = 0;
> + p->exe_file = current->exe_file;
> + if (p->exe_file)
> + get_file(p->exe_file);
>
> /*
> * Ok, make it visible to the rest of the system.
> * We dont wake it up yet.
> */
> @@ -1218,11 +1221,11 @@ static struct task_struct *copy_process(
> recalc_sigpending();
> if (signal_pending(current)) {
> spin_unlock(¤t->sighand->siglock);
> write_unlock_irq(&tasklist_lock);
> retval = -ERESTARTNOINTR;
> - goto bad_fork_cleanup_namespaces;
> + goto bad_fork_cleanup_exe_file;
> }
>
> if (clone_flags & CLONE_THREAD) {
> p->group_leader = current->group_leader;
> list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
> @@ -1274,10 +1277,15 @@ static struct task_struct *copy_process(
> put_user(p->pid, parent_tidptr);
>
> proc_fork_connector(p);
> return p;
>
> +bad_fork_cleanup_exe_file:
> + if (p->exe_file) {
> + fput(p->exe_file);
> + p->exe_file = NULL;
> + }
> bad_fork_cleanup_namespaces:
> exit_task_namespaces(p);
> bad_fork_cleanup_keys:
> exit_keys(p);
> bad_fork_cleanup_mm:
> Index: linux-2.6.22-rc2-mm1/fs/proc/task_mmu.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/fs/proc/task_mmu.c
> +++ linux-2.6.22-rc2-mm1/fs/proc/task_mmu.c
> @@ -71,44 +71,10 @@ int task_statm(struct mm_struct *mm, int
> *data = mm->total_vm - mm->shared_vm;
> *resident = *shared + get_mm_counter(mm, anon_rss);
> return mm->total_vm;
> }
>
> -int proc_exe_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
> -{
> - struct vm_area_struct * vma;
> - int result = -ENOENT;
> - struct task_struct *task = get_proc_task(inode);
> - struct mm_struct * mm = NULL;
> -
> - if (task) {
> - mm = get_task_mm(task);
> - put_task_struct(task);
> - }
> - if (!mm)
> - goto out;
> - down_read(&mm->mmap_sem);
> -
> - vma = mm->mmap;
> - while (vma) {
> - if ((vma->vm_flags & VM_EXECUTABLE) && vma->vm_file)
> - break;
> - vma = vma->vm_next;
> - }
> -
> - if (vma) {
> - *mnt = mntget(vma->vm_file->f_path.mnt);
> - *dentry = dget(vma->vm_file->f_path.dentry);
> - result = 0;
> - }
> -
> - up_read(&mm->mmap_sem);
> - mmput(mm);
> -out:
> - return result;
> -}
> -
> static void pad_len_spaces(struct seq_file *m, int len)
> {
> len = 25 + sizeof(void*) * 6 - len;
> if (len < 1)
> len = 1;
> Index: linux-2.6.22-rc2-mm1/fs/proc/task_nommu.c
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/fs/proc/task_nommu.c
> +++ linux-2.6.22-rc2-mm1/fs/proc/task_nommu.c
> @@ -102,44 +102,10 @@ int task_statm(struct mm_struct *mm, int
> up_read(&mm->mmap_sem);
> *resident = size;
> return size;
> }
>
> -int proc_exe_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
> -{
> - struct vm_list_struct *vml;
> - struct vm_area_struct *vma;
> - struct task_struct *task = get_proc_task(inode);
> - struct mm_struct *mm = get_task_mm(task);
> - int result = -ENOENT;
> -
> - if (!mm)
> - goto out;
> - down_read(&mm->mmap_sem);
> -
> - vml = mm->context.vmlist;
> - vma = NULL;
> - while (vml) {
> - if ((vml->vma->vm_flags & VM_EXECUTABLE) && vml->vma->vm_file) {
> - vma = vml->vma;
> - break;
> - }
> - vml = vml->next;
> - }
> -
> - if (vma) {
> - *mnt = mntget(vma->vm_file->f_path.mnt);
> - *dentry = dget(vma->vm_file->f_path.dentry);
> - result = 0;
> - }
> -
> - up_read(&mm->mmap_sem);
> - mmput(mm);
> -out:
> - return result;
> -}
> -
> /*
> * display mapping lines for a particular process's /proc/pid/maps
> */
> static int show_map(struct seq_file *m, void *_vml)
> {
> Index: linux-2.6.22-rc2-mm1/fs/proc/internal.h
> ===================================================================
> --- linux-2.6.22-rc2-mm1.orig/fs/proc/internal.h
> +++ linux-2.6.22-rc2-mm1/fs/proc/internal.h
> @@ -38,11 +38,10 @@ extern int nommu_vma_show(struct seq_fil
> #endif
>
> extern int maps_protect;
>
> extern void create_seq_entry(char *name, mode_t mode, const struct file_operations *f);
> -extern int proc_exe_link(struct inode *, struct dentry **, struct vfsmount **);
> extern int proc_tid_stat(struct task_struct *, char *);
> extern int proc_tgid_stat(struct task_struct *, char *);
> extern int proc_pid_status(struct task_struct *, char *);
> extern int proc_pid_statm(struct task_struct *, char *);
> extern loff_t mem_lseek(struct file * file, loff_t offset, int orig);
>
>
> -
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