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[PATCH] proc: Rewrite the proc dentry flush on exit optimization

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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 <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Eric W. Biederman
2006-06-26 00:25:48 -07:00
committed by Linus Torvalds
parent 662795deb8
commit 48e6484d49
7 changed files with 65 additions and 101 deletions
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136
fs/proc/base.c
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@@ -1352,16 +1352,6 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
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?
@@ -1383,13 +1373,6 @@ static struct dentry_operations pid_dentry_operations =
.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)
@@ -1859,57 +1842,70 @@ static struct inode_operations proc_self_inode_operations = {
};
/**
* 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.
*
* Drops the /proc/@pid dcache entry from the hash chains.
* @task: task that should be flushed.
*
* 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.
* 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.
*
* 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.
*
* 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;
proc_dentry = p->proc_dentry;
if (proc_dentry != NULL) {
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);
name.name = buf;
name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
dentry = d_hash_and_lookup(proc_mnt->mnt_root, &name);
if (dentry) {
shrink_dcache_parent(dentry);
d_drop(dentry);
dput(dentry);
}
return proc_dentry;
}
/**
* 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.
*/
void proc_pid_flush(struct dentry *proc_dentry)
{
might_sleep();
if(proc_dentry != NULL) {
shrink_dcache_parent(proc_dentry);
dput(proc_dentry);
if (thread_group_leader(task))
goto out;
name.name = buf;
name.len = snprintf(buf, sizeof(buf), "%d", task->tgid);
leader = d_hash_and_lookup(proc_mnt->mnt_root, &name);
if (!leader)
goto out;
name.name = "task";
name.len = strlen(name.name);
dir = d_hash_and_lookup(leader, &name);
if (!dir)
goto out_put_leader;
name.name = buf;
name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
dentry = d_hash_and_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 */
@@ -1919,7 +1915,6 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct
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);
@@ -1965,23 +1960,16 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct
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;
}
spin_unlock(&task->proc_lock);
put_task_struct(task);
if (died) {
proc_pid_flush(dentry);
d_drop(dentry);
shrink_dcache_parent(dentry);
goto out;
}
put_task_struct(task);
return NULL;
out:
return ERR_PTR(-ENOENT);
@@ -2024,7 +2012,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
inode->i_nlink = 3;
#endif
dentry->d_op = &pid_base_dentry_operations;
dentry->d_op = &pid_dentry_operations;
d_add(dentry, inode);