Messages in this thread Patch in this message | | | Date | Thu, 30 Jul 2009 23:29:56 +0200 | From | Oleg Nesterov <> | Subject | Re: Possible memory leak via alloc_pid() |
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On 07/29, Andrew Morton wrote: > > On Wed, 8 Jul 2009 22:33:31 +0100 > Catalin Marinas <catalin.marinas@arm.com> wrote: > > > Hi, > > > > There's a kmemleak report of a struct pid allocation in alloc_pid() > > which somehow gets lost: > > > > unreferenced object 0xc307aa00 (size 44): > > comm "gdm", pid 2734, jiffies 4294902040 > > backtrace: > > [<c01e721a>] create_object+0xfa/0x250 > > [<c01e73cd>] kmemleak_alloc+0x5d/0x70 > > [<c01e0ad6>] kmem_cache_alloc+0x156/0x1a0 > > [<c01552f9>] alloc_pid+0x19/0x350 > > [<c013e6e0>] copy_process+0x800/0x1230 > > [<c013f17f>] do_fork+0x6f/0x370 > > [<c0101986>] sys_clone+0x36/0x40 > > [<c010319c>] sysenter_do_call+0x12/0x38 > > [<ffffffff>] 0xffffffff > > > > This is the gdm fork for starting Xorg (with pid 2739). It first > > logged me in automatically, after which I logged out and gdm started > > another Xorg. The pid structure for the first Xorg is reported as a > > leak. The Xorg with pid 2739 is no longer present on my system. > > > > Using gdb vmlinux /proc/kcore shows that the pid->count is 2, so > > that's why it probably wasn't freed by put_pid(): > > > > (gdb) print ({struct pid}0xc307aa00) > > $20 = {count = {counter = 2}, level = 0, tasks = {{first = 0x0}, { > > first = 0x0}, {first = 0x0}}, rcu = {next = 0xc24bfd64, > > func = 0xc0154e90 <delayed_put_pid>}, numbers = {{nr = 2739, > > ns = 0xc0737540, pid_chain = {next = 0x0, pprev = 0x200200}}}} > > > > Note that kmemleak is aware of and scans pid_hash (which was recorded > > in kmemleak as a 16KB object).
This pid is detached and unhanshed. God knows who did the unbalanced get_pid().
Since you can reproduce the problem easily, perhaps you can use the hack above to track get/put ?
$ echo pid_of_Xorg > /proc/sys/kernel/xxx
Oleg.
--- CPUHP/kernel/sysctl.c~TRACK_PID 2009-06-28 18:14:27.000000000 +0200 +++ CPUHP/kernel/sysctl.c 2009-07-30 23:12:43.000000000 +0200 @@ -244,6 +244,10 @@ static int min_wakeup_granularity_ns; static int max_wakeup_granularity_ns = NSEC_PER_SEC; /* 1 second */ #endif +extern int xxx_pid; +int set_xxx_pid(struct ctl_table *, int, struct file *, + void __user *, size_t *, loff_t *); + static struct ctl_table kern_table[] = { #ifdef CONFIG_SCHED_DEBUG { @@ -989,7 +993,15 @@ static struct ctl_table kern_table[] = { .proc_handler = &proc_dointvec, }, #endif - + { + .ctl_name = 666, + .procname = "xxx", + .data = &xxx_pid, + .maxlen = sizeof (int), + .mode = 0666, + .proc_handler = &set_xxx_pid, + .strategy = sysctl_intvec, + }, /* * NOTE: do not add new entries to this table unless you have read * Documentation/sysctl/ctl_unnumbered.txt --- CPUHP/include/linux/pid.h~TRACK_PID 2009-04-06 00:03:41.000000000 +0200 +++ CPUHP/include/linux/pid.h 2009-07-30 23:10:32.000000000 +0200 @@ -57,6 +57,7 @@ struct upid { struct pid { atomic_t count; + int trackme; unsigned int level; /* lists of tasks that use this pid */ struct hlist_head tasks[PIDTYPE_MAX]; @@ -74,8 +75,14 @@ struct pid_link static inline struct pid *get_pid(struct pid *pid) { - if (pid) + if (pid) { + if (pid->trackme) { + printk(KERN_INFO "XXXXX(%d) ++%d\n", + pid->numbers[0].nr, atomic_read(&pid->count)); + dump_stack(); + } atomic_inc(&pid->count); + } return pid; } --- CPUHP/kernel/pid.c~TRACK_PID 2009-07-13 17:39:44.000000000 +0200 +++ CPUHP/kernel/pid.c 2009-07-30 23:12:05.000000000 +0200 @@ -207,6 +207,12 @@ void put_pid(struct pid *pid) if (!pid) return; + if (pid->trackme) { + printk(KERN_INFO "XXXXX(%d) --%d\n", + pid->numbers[0].nr, atomic_read(&pid->count)); + dump_stack(); + } + ns = pid->numbers[pid->level].ns; if ((atomic_read(&pid->count) == 1) || atomic_dec_and_test(&pid->count)) { @@ -250,6 +256,7 @@ struct pid *alloc_pid(struct pid_namespa pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); if (!pid) goto out; + pid->trackme = 0; tmp = ns; for (i = ns->level; i >= 0; i--) { @@ -491,6 +498,30 @@ struct pid *find_ge_pid(int nr, struct p return pid; } +int xxx_pid; + +int set_xxx_pid(ctl_table *table, int write, struct file *file, + void __user *buffer, size_t *length, loff_t *ppos) +{ + struct pid *pid; + + proc_dointvec_minmax(table, write, file, buffer, length, ppos); + if (!write) + return 0; + + rcu_read_lock(); + pid = find_vpid(xxx_pid); + if (pid) { + printk(KERN_INFO "XXXXX(%d) ==%d\n", xxx_pid, atomic_read(&pid->count)); + pid->trackme = 1; + } else { + printk(KERN_INFO "XXXXX(%d) not found\n", xxx_pid); + } + rcu_read_unlock(); + + return 0; +} + /* * The pid hash table is scaled according to the amount of memory in the * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
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