On Tue, 28 Jan 2003, Brian Sullivan wrote:
> The problem I am experiencing is that after a certain number of mounts I
> get the error message "fork: Resource temporarily unavailable" on the
> command line.
> After much trouble shooting I realized that number of mounts/umount
> sequences I am limited to is the max number of processes for my user id. I
> confirmed this by using the "ulimit -u" command to lower my process limit.
> It appears the mount command is leaving someting in some sort of process
> table in kernel memory (nothing shows in ps or top or in /proc/#### as
> being left behind). Has anybody any sort of experience with this at all?
> Any suggestions?
It's a kernel bug (and easy to reproduce).
Every time you do a loop mount, a kernel thread is started (those
processes are called "loop0", "loop1", etc.). The problem is that when
it starts, it's counted as one of your processes *). Then, it's
changed to be a root-owned process without correcting that count **).
Patch below fixes the problem. It moves the bookkeeping of changing
current->user to a new function switch_uid() (which is now also used
by exec_usermodehelper() in kmod.c). The patch is tested.
Eric
*) "atomic_inc(&p->user->processes);" in do_fork().
**) "this_task->user = INIT_USER;" in reparent_to_init().
--- linux-2.4.21-pre3/include/linux/sched.h.orig 2003-01-28 21:39:29.000000000
+0100
+++ linux-2.4.21-pre3/include/linux/sched.h 2003-01-28 22:26:29.000000000 +0100
@@ -576,6 +576,7 @@
/* per-UID process charging. */
extern struct user_struct * alloc_uid(uid_t);
extern void free_uid(struct user_struct *);
+extern void switch_uid(struct user_struct *);
#include <asm/current.h>
--- linux-2.4.21-pre3/kernel/sys.c.orig 2003-01-28 21:21:20.000000000 +0100
+++ linux-2.4.21-pre3/kernel/sys.c 2003-01-28 22:30:13.000000000 +0100
@@ -492,19 +492,12 @@
static int set_user(uid_t new_ruid, int dumpclear)
{
- struct user_struct *new_user, *old_user;
+ struct user_struct *new_user;
- /* What if a process setreuid()'s and this brings the
- * new uid over his NPROC rlimit? We can check this now
- * cheaply with the new uid cache, so if it matters
- * we should be checking for it. -DaveM
- */
new_user = alloc_uid(new_ruid);
if (!new_user)
return -EAGAIN;
- old_user = current->user;
- atomic_dec(&old_user->processes);
- atomic_inc(&new_user->processes);
+ switch_uid(new_user);
if(dumpclear)
{
@@ -512,8 +505,6 @@
wmb();
}
current->uid = new_ruid;
- current->user = new_user;
- free_uid(old_user);
return 0;
}
--- linux-2.4.21-pre3/kernel/sched.c.orig 2003-01-28 21:21:06.000000000 +0100
+++ linux-2.4.21-pre3/kernel/sched.c 2003-01-28 22:30:41.000000000 +0100
@@ -1274,7 +1274,7 @@
this_task->cap_permitted = CAP_FULL_SET;
this_task->keep_capabilities = 0;
memcpy(this_task->rlim, init_task.rlim, sizeof(*(this_task->rlim)));
- this_task->user = INIT_USER;
+ switch_uid(INIT_USER);
spin_unlock(&runqueue_lock);
write_unlock_irq(&tasklist_lock);
--- linux-2.4.21-pre3/kernel/kmod.c.orig 2003-01-28 22:29:02.000000000 +0100
+++ linux-2.4.21-pre3/kernel/kmod.c 2003-01-28 22:29:36.000000000 +0100
@@ -119,15 +119,7 @@
if (curtask->files->fd[i]) close(i);
}
- /* Drop the "current user" thing */
- {
- struct user_struct *user = curtask->user;
- curtask->user = INIT_USER;
- atomic_inc(&INIT_USER->__count);
- atomic_inc(&INIT_USER->processes);
- atomic_dec(&user->processes);
- free_uid(user);
- }
+ switch_uid(INIT_USER);
/* Give kmod all effective privileges.. */
curtask->euid = curtask->fsuid = 0;
--- linux-2.4.21-pre3/kernel/user.c.orig 2003-01-28 22:23:21.000000000 +0100
+++ linux-2.4.21-pre3/kernel/user.c 2003-01-28 22:37:48.000000000 +0100
@@ -120,6 +120,23 @@
return up;
}
+void switch_uid(struct user_struct *new_user)
+{
+ struct user_struct *old_user;
+
+ /* What if a process setreuid()'s and this brings the
+ * new uid over his NPROC rlimit? We can check this now
+ * cheaply with the new uid cache, so if it matters
+ * we should be checking for it. -DaveM
+ */
+ old_user = current->user;
+ atomic_inc(&new_user->__count);
+ atomic_inc(&new_user->processes);
+ atomic_dec(&old_user->processes);
+ current->user = new_user;
+ free_uid(old_user);
+}
+
static int __init uid_cache_init(void)
{
--
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