Re: [RFC PATCH 3/5] pgo: Wire up the new more generic code for modules

[jarmo . tiitto]

Kees Cook wrote maanantaina 14. kesäkuuta 2021 18.55.23 EEST:
> On Sat, Jun 12, 2021 at 06:24:24AM +0300, Jarmo Tiitto wrote:
> > prf_open() now uses the inode->i_private to get
> > the prf_object for the file. This can be either
> > vmlinux.profraw or any module.profraw file.
> > 
> > The prf_vmlinux object is now added into prf_list and
> > allocate_node() scans the list and reserves vnodes
> > from corresponding prf_object(s).
> > 
> > Signed-off-by: Jarmo Tiitto <jarmo.tiitto@xxxxxxxxx>
> > ---
> > note: There is no module notifier code yet,
> > so only vmlinux.profraw profile data
> > is available with this commit.
> > 
> > Another thing is that pgo/reset will only
> > reset vmlinux.profraw.
> > Profile data reset for modules may be added later:
> > maybe writing module's name into pgo/reset would reset only
> > the specified module's profile data?
> > Then writing "all" or zero would atomically reset everything.
> 
> Yeah, I think matching the internal naming is right. "vmlinux",
> module::name, and "all"?
> 
> > I'm bit unsure about the new allocate_node() code since
> > it is the first place I had to put rcu_read_lock()
> > and the code is likely to change from this.
> 
> Comments below...
> 
> > ---
> > 
> >  kernel/pgo/fs.c         | 30 ++++++++++++++++++++-----
> >  kernel/pgo/instrument.c | 49 +++++++++++++++++++++++++++--------------
> >  kernel/pgo/pgo.h        |  2 ++
> >  3 files changed, 60 insertions(+), 21 deletions(-)
> > 
> > diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
> > index 7e269d69bcd7..84b36e61758b 100644
> > --- a/kernel/pgo/fs.c
> > +++ b/kernel/pgo/fs.c
> > @@ -32,8 +32,10 @@ static struct dentry *directory;
> > 
> >  struct prf_private_data {
> >  
> >  	void *buffer;
> >  	size_t size;
> > 
> > +	struct prf_object *core;
> > 
> >  };
> > 
> > +/* vmlinux's prf core */
> > 
> >  static struct prf_object prf_vmlinux;
> >  
> >  /*
> > 
> > @@ -281,7 +283,6 @@ static int prf_serialize(struct prf_object *po, struct
> > prf_private_data *p, size> 
> >  	prf_serialize_values(po, &buffer);
> >  	
> >  	return 0;
> > 
> > -
> > 
> >  }
> >  
> >  /* open() implementation for PGO. Creates a copy of the profiling data 
set.
> >  */> 
> > @@ -292,13 +293,21 @@ static int prf_open(struct inode *inode, struct file
> > *file)> 
> >  	size_t buf_size;
> >  	int err = -EINVAL;
> > 
> > +	if (WARN_ON(!inode->i_private)) {
> > +		/* bug: inode was not initialized by us */
> > +		return err;
> > +	}
> > +
> > 
> >  	data = kzalloc(sizeof(*data), GFP_KERNEL);
> >  	if (!data)
> >  	
> >  		return -ENOMEM;
> > 
> > +	/* Get prf_object of this inode */
> > +	data->core = inode->i_private;
> > +
> > 
> >  	/* Get initial buffer size. */
> >  	flags = prf_lock();
> > 
> > -	data->size = prf_buffer_size(&prf_vmlinux);
> > +	data->size = prf_buffer_size(data->core);
> > 
> >  	prf_unlock(flags);
> >  	
> >  	do {
> > 
> > @@ -318,12 +327,13 @@ static int prf_open(struct inode *inode, struct file
> > *file)> 
> >  		 * data length in data->size.
> >  		 */
> >  		
> >  		flags = prf_lock();
> > 
> > -		err = prf_serialize(&prf_vmlinux, data, buf_size);
> > +		err = prf_serialize(data->core, data, buf_size);
> > 
> >  		prf_unlock(flags);
> >  		/* In unlikely case, try again. */
> >  	
> >  	} while (err == -EAGAIN);
> >  	
> >  	if (err < 0) {
> > 
> > +
> > 
> >  		if (data)
> >  		
> >  			vfree(data->buffer);
> >  		
> >  		kfree(data);
> > 
> > @@ -412,6 +422,8 @@ static const struct file_operations prf_reset_fops = {
> > 
> >  /* Create debugfs entries. */
> >  static int __init pgo_init(void)
> >  {
> > 
> > +	unsigned long flags;
> > +
> > 
> >  	/* Init profiler vmlinux core entry */
> >  	memset(&prf_vmlinux, 0, sizeof(prf_vmlinux));
> >  	prf_vmlinux.data = __llvm_prf_data_start;
> > 
> > @@ -430,19 +442,27 @@ static int __init pgo_init(void)
> > 
> >  	prf_vmlinux.vnds_num = prf_get_count(__llvm_prf_vnds_start,
> >  	
> >  		__llvm_prf_vnds_end, 
sizeof(__llvm_prf_vnds_start[0]));
> > 
> > +	/* enable profiling */
> > +	flags = prf_list_lock();
> > +	list_add_tail_rcu(&prf_vmlinux.link, &prf_list);
> > +	prf_list_unlock(flags);
> > 
> >  	directory = debugfs_create_dir("pgo", NULL);
> >  	if (!directory)
> >  	
> >  		goto err_remove;
> > 
> > -	if (!debugfs_create_file("vmlinux.profraw", 0600, directory, NULL,
> > -				 &prf_fops))
> > +	prf_vmlinux.file = debugfs_create_file("vmlinux.profraw",
> > +		0600, directory, &prf_vmlinux, &prf_fops);
> > +	if (!prf_vmlinux.file)
> > 
> >  		goto err_remove;
> >  	
> >  	if (!debugfs_create_file("reset", 0200, directory, NULL,
> >  	
> >  				 &prf_reset_fops))
> >  		
> >  		goto err_remove;
> > 
> > +	/* show notice why the system slower: */
> > +	pr_notice("Clang PGO instrumentation is active.");
> > +
> 
> Please pull this change into a separate patch and make it pr_info()
> ("notice" is, I think, not right here).
> 

All rightly then.

> >  	return 0;
> >  
> >  err_remove:
> > diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> > index 24fdeb79b674..e214c9d7a113 100644
> > --- a/kernel/pgo/instrument.c
> > +++ b/kernel/pgo/instrument.c
> > @@ -24,6 +24,7 @@
> > 
> >  #include <linux/export.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/types.h>
> > 
> > +#include <linux/rculist.h>
> > 
> >  #include "pgo.h"
> >  
> >  /*
> > 
> > @@ -56,22 +57,38 @@ void prf_unlock(unsigned long flags)
> > 
> >  static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> >  
> >  						 
u32 index, u64 value)
> >  
> >  {
> > 
> > -	const int max_vnds = prf_get_count(__llvm_prf_vnds_start,
> > -		__llvm_prf_vnds_end, sizeof(struct 
llvm_prf_value_node));
> > -
> > -	/*
> > -	 * Check that p is within vmlinux __llvm_prf_data section.
> > -	 * If not, don't allocate since we can't handle modules yet.
> > -	 */
> > -	if (!memory_contains(__llvm_prf_data_start,
> > -		__llvm_prf_data_end, p, sizeof(*p)))
> > -		return NULL;
> > -
> > -	if (WARN_ON_ONCE(current_node >= max_vnds))
> > -		return NULL; /* Out of nodes */
> > -
> > -	/* reserve vnode for vmlinux */
> > -	return &__llvm_prf_vnds_start[current_node++];
> > +	struct llvm_prf_value_node *vnode = NULL;
> > +	struct prf_object *po;
> > +	struct llvm_prf_data *data_end;
> > +	int max_vnds;
> > +
> > +	rcu_read_lock();
> 
> AIUI, list readers are using rcu_read_lock(), and writers are using
> prf_list_lock()?
> 

Yes, I intended the list readers to use rcu_read_lock() and writers to take 
the prf_list_lock().

Sadly after I sent this patch set I found during more testing that there are 
few problems that I need to work on:

There is an lockup that only occurs during bare metal run after +15min, so I 
haven't been able to catch it in VM.
I suspect this is caused by the RCU locking I added such that it results in 
recursive calls into __llvm_profile_instrument_target()

I will try build with CONFIG_PROVE_LOCKING, but I have had problems with
the kernel not getting past cgroup_init_early()... even without my patches
applied. (stock -rc kernel) :-(

> > +
> > +	list_for_each_entry_rcu(po, &prf_list, link) {
> > +		/* get section limits */
> > +		max_vnds = prf_vnds_count(po);
> > +		data_end = po->data + prf_data_count(po);
> > +
> > +		/*
> > +		 * Check that p is within:
> > +		 * [po->data, po->data + prf_data_count(po)] section.
> > +		 * If yes, allocate vnode from this prf_object.
> > +		 */
> > +		if (memory_contains(po->data, data_end, p, 
sizeof(*p))) {
> > +
> > +
> > +			if (WARN_ON_ONCE(po->current_node >= 
max_vnds))
> > +				return NULL; /* Out of 
nodes */
> > +
> > +			/* reserve the vnode */
> > +			vnode = &po->vnds[po->current_node++];
> > +			goto out;
> > +		}
> > +	}
> > +
> > +out:
> > +	rcu_read_unlock();
> > +	return vnode;
> > 
> >  }
> >  
> >  /*
> > 
> > diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> > index 44d79e2861e1..59d0aa966fbe 100644
> > --- a/kernel/pgo/pgo.h
> > +++ b/kernel/pgo/pgo.h
> > @@ -19,6 +19,8 @@
> > 
> >  #ifndef _PGO_H
> >  #define _PGO_H
> > 
> > +#include <linux/rculist.h>
> > +
> > 
> >  /*
> >  
> >   * Note: These internal LLVM definitions must match the compiler version.
> >   * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source
> >   code.
> > 
> > --
> > 2.32.0
> 
> --
> Kees Cook