To keep the dcache from filling up with dead /proc entries we flush
them on process exit. However over the years that code has gotten
hairy with a dentry pointer and a lock in task_struct and
misdocumented as a correctness feature.
I have rewritten this code to look and see if we have a corresponding
entry in the dcache and if so flush it on process exit. This removes
the extra fields in the task_struct and allows me to trivially handle
the case of a /proc/<tgid>/task/<pid> entry as well as the current
/proc/<pid> entries.
Signed-off-by: Eric W. Biederman <[email protected]>
---
fs/exec.c | 9 ---
fs/proc/base.c | 143 ++++++++++++++++++++++-----------------------
include/linux/init_task.h | 1
include/linux/proc_fs.h | 6 +-
include/linux/sched.h | 3 -
kernel/exit.c | 12 ----
kernel/fork.c | 3 -
7 files changed, 72 insertions(+), 105 deletions(-)
8ab2fe374434b424ef579e6e8d644a2b81ec4459
diff --git a/fs/exec.c b/fs/exec.c
index fc1c7a2..8033939 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -657,7 +657,6 @@ static int de_thread(struct task_struct
*/
if (!thread_group_leader(current)) {
struct task_struct *parent;
- struct dentry *proc_dentry1, *proc_dentry2;
unsigned long ptrace;
/*
@@ -669,10 +668,6 @@ static int de_thread(struct task_struct
while (leader->exit_state != EXIT_ZOMBIE)
yield();
- spin_lock(&leader->proc_lock);
- spin_lock(¤t->proc_lock);
- proc_dentry1 = proc_pid_unhash(current);
- proc_dentry2 = proc_pid_unhash(leader);
write_lock_irq(&tasklist_lock);
BUG_ON(leader->tgid != current->tgid);
@@ -729,10 +724,6 @@ static int de_thread(struct task_struct
leader->exit_state = EXIT_DEAD;
write_unlock_irq(&tasklist_lock);
- spin_unlock(&leader->proc_lock);
- spin_unlock(¤t->proc_lock);
- proc_pid_flush(proc_dentry1);
- proc_pid_flush(proc_dentry2);
}
/*
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4bdc859..9fab7fe 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -911,7 +911,7 @@ static int proc_check_dentry_visible(str
/* See if the the two tasks share a commone set of
* file descriptors. If so everything is visible.
*/
- task = get_proc_task(inode);
+ task = proc_task(inode);
if (!task)
goto out;
files = get_files_struct(current);
@@ -922,7 +922,6 @@ static int proc_check_dentry_visible(str
put_files_struct(task_files);
if (files)
put_files_struct(files);
- put_task_struct(task);
if (!error)
goto out;
@@ -1291,16 +1290,6 @@ static int tid_fd_revalidate(struct dent
return 0;
}
-static void pid_base_iput(struct dentry *dentry, struct inode *inode)
-{
- struct task_struct *task = proc_task(inode);
- spin_lock(&task->proc_lock);
- if (task->proc_dentry == dentry)
- task->proc_dentry = NULL;
- spin_unlock(&task->proc_lock);
- iput(inode);
-}
-
static int pid_delete_dentry(struct dentry * dentry)
{
/* Is the task we represent dead?
@@ -1322,13 +1311,6 @@ static struct dentry_operations pid_dent
.d_delete = pid_delete_dentry,
};
-static struct dentry_operations pid_base_dentry_operations =
-{
- .d_revalidate = pid_revalidate,
- .d_iput = pid_base_iput,
- .d_delete = pid_delete_dentry,
-};
-
/* Lookups */
static unsigned name_to_int(struct dentry *dentry)
@@ -1787,57 +1769,78 @@ static struct inode_operations proc_self
};
/**
- * proc_pid_unhash - Unhash /proc/@pid entry from the dcache.
- * @p: task that should be flushed.
+ * proc_flush_task - Remove dcache entries for @task from the /proc dcache.
+ *
+ * @task: task that should be flushed.
+ *
+ * Looks in the dcache for
+ * /proc/@pid
+ * /proc/@tgid/task/@pid
+ * if either directory is present flushes it and all of it'ts children
+ * from the dcache.
*
- * Drops the /proc/@pid dcache entry from the hash chains.
+ * It is safe and reasonable to cache /proc entries for a task until
+ * that task exits. After that they just clog up the dcache with
+ * useless entries, possibly causing useful dcache entries to be
+ * flushed instead. This routine is proved to flush those useless
+ * dcache entries at process exit time.
*
- * Dropping /proc/@pid entries and detach_pid must be synchroneous,
- * otherwise e.g. /proc/@pid/exe might point to the wrong executable,
- * if the pid value is immediately reused. This is enforced by
- * - caller must acquire spin_lock(p->proc_lock)
- * - must be called before detach_pid()
- * - proc_pid_lookup acquires proc_lock, and checks that
- * the target is not dead by looking at the attach count
- * of PIDTYPE_PID.
+ * NOTE: This routine is just an optimization so it does not guarantee
+ * that no dcache entries will exist at process exit time it
+ * just makes it very unlikely that any will persist.
*/
-
-struct dentry *proc_pid_unhash(struct task_struct *p)
+void proc_flush_task(struct task_struct *task)
{
- struct dentry *proc_dentry;
+ struct dentry *dentry, *leader, *dir;
+ char buf[30];
+ struct qstr name;
+
+ name.name = buf;
+ name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
+ name.hash = full_name_hash(name.name, name.len);
+
+ dentry = d_lookup(proc_mnt->mnt_root, &name);
+ if (dentry) {
+ shrink_dcache_parent(dentry);
+ d_drop(dentry);
+ dput(dentry);
+ }
+
+ if (thread_group_leader(task))
+ goto out;
- proc_dentry = p->proc_dentry;
- if (proc_dentry != NULL) {
+ name.name = buf;
+ name.len = snprintf(buf, sizeof(buf), "%d", task->tgid);
+ name.hash = full_name_hash(name.name, name.len);
- spin_lock(&dcache_lock);
- spin_lock(&proc_dentry->d_lock);
- if (!d_unhashed(proc_dentry)) {
- dget_locked(proc_dentry);
- __d_drop(proc_dentry);
- spin_unlock(&proc_dentry->d_lock);
- } else {
- spin_unlock(&proc_dentry->d_lock);
- proc_dentry = NULL;
- }
- spin_unlock(&dcache_lock);
- }
- return proc_dentry;
-}
+ leader = d_lookup(proc_mnt->mnt_root, &name);
+ if (!leader)
+ goto out;
-/**
- * proc_pid_flush - recover memory used by stale /proc/@pid/x entries
- * @proc_dentry: directoy to prune.
- *
- * Shrink the /proc directory that was used by the just killed thread.
- */
+ name.name = "task";
+ name.len = strlen(name.name);
+ name.hash = full_name_hash(name.name, name.len);
-void proc_pid_flush(struct dentry *proc_dentry)
-{
- might_sleep();
- if(proc_dentry != NULL) {
- shrink_dcache_parent(proc_dentry);
- dput(proc_dentry);
+ dir = d_lookup(leader, &name);
+ if (!dir)
+ goto out_put_leader;
+
+ name.name = buf;
+ name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
+ name.hash = full_name_hash(name.name, name.len);
+
+ dentry = d_lookup(dir, &name);
+ if (dentry) {
+ shrink_dcache_parent(dentry);
+ d_drop(dentry);
+ dput(dentry);
}
+
+ dput(dir);
+out_put_leader:
+ dput(leader);
+out:
+ return;
}
/* SMP-safe */
@@ -1847,7 +1850,6 @@ struct dentry *proc_pid_lookup(struct in
struct inode *inode;
struct proc_inode *ei;
unsigned tgid;
- int died;
if (dentry->d_name.len == 4 && !memcmp(dentry->d_name.name,"self",4)) {
inode = new_inode(dir->i_sb);
@@ -1893,23 +1895,16 @@ struct dentry *proc_pid_lookup(struct in
inode->i_nlink = 4;
#endif
- dentry->d_op = &pid_base_dentry_operations;
+ dentry->d_op = &pid_dentry_operations;
- died = 0;
d_add(dentry, inode);
- spin_lock(&task->proc_lock);
- task->proc_dentry = dentry;
if (!pid_alive(task)) {
- dentry = proc_pid_unhash(task);
- died = 1;
+ d_drop(dentry);
+ shrink_dcache_parent(dentry);
+ goto out;
}
- spin_unlock(&task->proc_lock);
put_task_struct(task);
- if (died) {
- proc_pid_flush(dentry);
- goto out;
- }
return NULL;
out:
return ERR_PTR(-ENOENT);
@@ -1952,7 +1947,7 @@ static struct dentry *proc_task_lookup(s
inode->i_nlink = 3;
#endif
- dentry->d_op = &pid_base_dentry_operations;
+ dentry->d_op = &pid_dentry_operations;
d_add(dentry, inode);
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index dcfd2ec..62deb30 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -117,7 +117,6 @@ extern struct group_info init_groups;
.signal = {{0}}}, \
.blocked = {{0}}, \
.alloc_lock = SPIN_LOCK_UNLOCKED, \
- .proc_lock = SPIN_LOCK_UNLOCKED, \
.journal_info = NULL, \
.cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
.fs_excl = ATOMIC_INIT(0), \
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index cab152d..302c24e 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -97,9 +97,8 @@ extern void proc_misc_init(void);
struct mm_struct;
+void proc_flush_task(struct task_struct *task);
struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *);
-struct dentry *proc_pid_unhash(struct task_struct *p);
-void proc_pid_flush(struct dentry *proc_dentry);
int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir);
unsigned long task_vsize(struct mm_struct *);
int task_statm(struct mm_struct *, int *, int *, int *, int *);
@@ -209,8 +208,7 @@ static inline void proc_net_remove(const
#define proc_net_create(name, mode, info) ({ (void)(mode), NULL; })
static inline void proc_net_remove(const char *name) {}
-static inline struct dentry *proc_pid_unhash(struct task_struct *p) { return NULL; }
-static inline void proc_pid_flush(struct dentry *proc_dentry) { }
+static inline void proc_flush_task(struct task_struct *task) { }
static inline struct proc_dir_entry *create_proc_entry(const char *name,
mode_t mode, struct proc_dir_entry *parent) { return NULL; }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b6f51e3..9fb7688 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -824,8 +824,6 @@ struct task_struct {
u32 self_exec_id;
/* Protection of (de-)allocation: mm, files, fs, tty, keyrings */
spinlock_t alloc_lock;
-/* Protection of proc_dentry: nesting proc_lock, dcache_lock, write_lock_irq(&tasklist_lock); */
- spinlock_t proc_lock;
#ifdef CONFIG_DEBUG_MUTEXES
/* mutex deadlock detection */
@@ -838,7 +836,6 @@ struct task_struct {
/* VM state */
struct reclaim_state *reclaim_state;
- struct dentry *proc_dentry;
struct backing_dev_info *backing_dev_info;
struct io_context *io_context;
diff --git a/kernel/exit.c b/kernel/exit.c
index 531aadc..64956e0 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -63,12 +63,9 @@ void release_task(struct task_struct * p
{
int zap_leader;
task_t *leader;
- struct dentry *proc_dentry;
repeat:
atomic_dec(&p->user->processes);
- spin_lock(&p->proc_lock);
- proc_dentry = proc_pid_unhash(p);
write_lock_irq(&tasklist_lock);
if (unlikely(p->ptrace))
__ptrace_unlink(p);
@@ -104,8 +101,7 @@ repeat:
sched_exit(p);
write_unlock_irq(&tasklist_lock);
- spin_unlock(&p->proc_lock);
- proc_pid_flush(proc_dentry);
+ proc_flush_task(p);
release_thread(p);
put_task_struct(p);
@@ -118,15 +114,9 @@ repeat:
void unhash_process(struct task_struct *p)
{
- struct dentry *proc_dentry;
-
- spin_lock(&p->proc_lock);
- proc_dentry = proc_pid_unhash(p);
write_lock_irq(&tasklist_lock);
__unhash_process(p);
write_unlock_irq(&tasklist_lock);
- spin_unlock(&p->proc_lock);
- proc_pid_flush(proc_dentry);
}
/*
diff --git a/kernel/fork.c b/kernel/fork.c
index 3f56d5a..fae6510 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -984,13 +984,10 @@ static task_t *copy_process(unsigned lon
if (put_user(p->pid, parent_tidptr))
goto bad_fork_cleanup;
- p->proc_dentry = NULL;
-
INIT_LIST_HEAD(&p->children);
INIT_LIST_HEAD(&p->sibling);
p->vfork_done = NULL;
spin_lock_init(&p->alloc_lock);
- spin_lock_init(&p->proc_lock);
clear_tsk_thread_flag(p, TIF_SIGPENDING);
init_sigpending(&p->pending);
--
1.2.2.g709a
-
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