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 the
task lock, 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]>
---
Changelog:
Hold task_lock() while using task->exe_file. With this change I haven't
been able to reproduce Chris Wright's Oops report:
http://lkml.org/lkml/2007/5/31/34
I used a 4-way, x86 system running kernbench. I also tried a 4-way
x86_64
system running pidof. I used oprofile during all runs but I could not
reproduce Chris' Oops with the new patch.
Compiled and passed simple tests for regressions when patched against a 2.6.20
and a 2.6.22 kernel. Regression tests included a variety of file operations on
/proc/<pid|self>/exe such as stat, lstat, open, close, readlink, and unlink. All
produced the expected, baseline output results.
Andrew, please consider this patch for inclusion in -mm.
fs/exec.c | 7 +++++--
fs/proc/base.c | 21 +++++++++++++++++++++
fs/proc/internal.h | 1 -
fs/proc/task_mmu.c | 34 ----------------------------------
fs/proc/task_nommu.c | 34 ----------------------------------
include/linux/sched.h | 3 ++-
kernel/exit.c | 6 ++++++
kernel/fork.c | 9 ++++++++-
8 files changed, 42 insertions(+), 73 deletions(-)
Index: linux-2.6.22/include/linux/sched.h
===================================================================
--- linux-2.6.22.orig/include/linux/sched.h
+++ linux-2.6.22/include/linux/sched.h
@@ -937,10 +937,11 @@ 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;
@@ -1490,11 +1491,11 @@ static inline int thread_group_empty(str
#define delay_group_leader(p) \
(thread_group_leader(p) && !thread_group_empty(p))
/*
- * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
+ * Protects ->fs, ->files, ->mm, ->group_info, ->comm, ->exe_file, keyring
* subscriptions and synchronises with wait4(). Also used in procfs. Also
* pins the final release of task.io_context. Also protects ->cpuset.
*
* Nests both inside and outside of read_lock(&tasklist_lock).
* It must not be nested with write_lock_irq(&tasklist_lock),
Index: linux-2.6.22/fs/exec.c
===================================================================
--- linux-2.6.22.orig/fs/exec.c
+++ linux-2.6.22/fs/exec.c
@@ -1106,12 +1106,15 @@ 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);
+ task_lock(current);
+ if (current->exe_file)
+ fput(current->exe_file);
+ current->exe_file = bprm->file;
+ task_unlock(current);
bprm->file = NULL;
current->did_exec = 1;
proc_exec_connector(current);
return retval;
}
Index: linux-2.6.22/fs/proc/base.c
===================================================================
--- linux-2.6.22.orig/fs/proc/base.c
+++ linux-2.6.22/fs/proc/base.c
@@ -927,10 +927,31 @@ static const struct file_operations proc
.read = proc_fault_inject_read,
.write = proc_fault_inject_write,
};
#endif
+static int proc_exe_link(struct inode *inode, struct dentry **dentry,
+ struct vfsmount **mnt)
+{
+ int error = -ENOENT;
+ struct task_struct *task;
+
+ task = get_proc_task(inode);
+ if (!task)
+ return error;
+ task_lock(task);
+ 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:
+ task_unlock(task);
+ 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/kernel/exit.c
===================================================================
--- linux-2.6.22.orig/kernel/exit.c
+++ linux-2.6.22/kernel/exit.c
@@ -941,10 +941,16 @@ fastcall NORET_TYPE void do_exit(long co
if (unlikely(tsk->audit_context))
audit_free(tsk);
taskstats_exit(tsk, group_dead);
+ task_lock(tsk);
+ if (tsk->exe_file) {
+ fput(tsk->exe_file);
+ tsk->exe_file = NULL;
+ }
+ task_unlock(tsk);
exit_mm(tsk);
if (group_dead)
acct_process();
exit_sem(tsk);
Index: linux-2.6.22/kernel/fork.c
===================================================================
--- linux-2.6.22.orig/kernel/fork.c
+++ linux-2.6.22/kernel/fork.c
@@ -1164,10 +1164,12 @@ 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;
+ if (p->exe_file) /* ptr copied in dup_task_struct still needs a ref */
+ get_file(p->exe_file);
/*
* Ok, make it visible to the rest of the system.
* We dont wake it up yet.
*/
@@ -1219,11 +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);
@@ -1267,10 +1269,15 @@ static struct task_struct *copy_process(
spin_unlock(¤t->sighand->siglock);
write_unlock_irq(&tasklist_lock);
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/fs/proc/task_mmu.c
===================================================================
--- linux-2.6.22.orig/fs/proc/task_mmu.c
+++ linux-2.6.22/fs/proc/task_mmu.c
@@ -70,44 +70,10 @@ 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/fs/proc/task_nommu.c
===================================================================
--- linux-2.6.22.orig/fs/proc/task_nommu.c
+++ linux-2.6.22/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/fs/proc/internal.h
===================================================================
--- linux-2.6.22.orig/fs/proc/internal.h
+++ linux-2.6.22/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 *);
-
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