[lttng-dev] [PATCH lttng-ust v2] Fix: allocate ts_end in ringbuffer shared memory

Fri May 10 14:08:51 EDT 2019

Hi,

On Fri, May 10, 2019 at 12:33:42PM -0400, Sebastien Boisvert wrote:
> On 2019-05-10 11:26 a.m., Gabriel-Andrew Pollo-Guilbert wrote:
> 
> Hello Gabriel-Andrew,
> 
> > This patch allocates the memory used by the ts_end field added by commit
> > 6c737d05. When allocating lots of subbuffer for a channel (512 or more),
> > zalloc_shm() will fail to allocate all the objects because the allocated memory
> > map didn't take account the newly added field.
> > 
> > lttng-tools version: b14f53d4 (2.12.0-pre)
> > 
> > Steps to reproduce the bug:
> > 
> > 	1. lttng-sessiond -vvv --verbose-consumer
> 
> I need to killall existing lttng-sessiond daemon, right ?

No, since we are in userspace this can be done with a root lttng-sessiond
present. But in real life -> yes.

> 
> > 	2. start a traced application
> 
> I used lttng-ust/doc/examples/demo/.

Make sure that the app is long lived (easy-ust with a while loop for example).
This is only to force the allocation on lttng start.

> 
> > 	3. lttng create "test-sesssion"
>                                 ^^^
> There are too many s in session.

Does not matter since it is the session name here and subsequent call are done
in the context on that session. Still a good catch.

> 
> 
> > 	4. lttng enable-channel --userspace --num-subbuf 512 --subbuf-size 8k --overwrite channel
> > 	5. lttng enable-event -u -a -c channel
> > 	6. lttng start
> > 
> > After these steps, the following error message show should be thrown:
> > 
> > 	Error: ask_channel_creation consumer command failed
> > 	Error: Error creating UST channel "channel" on the consumer daemon
> 
> When I build lttng-tools b14f53d4
> 
> I get this error:
> 
> make[3]: Entering directory '/home/sboisvert/open-source/lttng.org/Source/lttng-tools/src/common/ust-consumer'
>   CC       ust-consumer.lo
> ust-consumer.c: In function 'lttng_ustconsumer_recv_cmd':
> ust-consumer.c:1459:7: error: 'struct ustctl_consumer_channel_attr' has no member named 'blocking_timeout'
>    attr.blocking_timeout= msg.u.ask_channel.blocking_timeout;
>        ^
> ust-consumer.c: In function 'lttng_ustconsumer_sample_snapshot_positions':
> ust-consumer.c:2225:9: warning: implicit declaration of function 'ustctl_snapshot_sample_positions'; did you mean 'ustctl_snapshot_get_produced'? [-Wimplicit-function-declaration]
>   return ustctl_snapshot_sample_positions(stream->ustream);
>          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>          ustctl_snapshot_get_produced
> Makefile:548: recipe for target 'ust-consumer.lo' failed

Are you sure you are building lttng-tools against lttng-ust
6c737d0594cac0d969e1948ea1ed55c15be9cec8 or master?

In any case, this does not seems related to this particular issue. Please start
a new email thread.

> 
> 
> There seems to be 2 declarations of struct ustctl_consumer_channel_attr.
> 
> In file lttng-tools/src/bin/lttng-sessiond/lttng-ust-ctl.h,
> struct ustctl_consumer_channel_attr has the attribute blocking_timeout.
> 
> In file lttng-ust/include/lttng/ust-ctl.h, struct ustctl_consumer_channel_attr
> does not have the attribute.

Currently on 6c737d0594cac0d969e1948ea1ed55c15be9cec8 (almost master):

struct ustctl_consumer_channel_attr {
	enum lttng_ust_chan_type type;
	uint64_t subbuf_size;			/* bytes */
	uint64_t num_subbuf;			/* power of 2 */
	int overwrite;				/* 1: overwrite, 0: discard */
	unsigned int switch_timer_interval;	/* usec */
	unsigned int read_timer_interval;	/* usec */
	enum lttng_ust_output output;		/* splice, mmap */
	uint32_t chan_id;			/* channel ID */
	unsigned char uuid[LTTNG_UST_UUID_LEN]; /* Trace session unique ID */
	int64_t blocking_timeout;			/* Blocking timeout (usec) */
} LTTNG_PACKED;

This field was introduced in b2c5f61a9. Suggesting that you lttng-ust tree is
out of date.

> 
> 
> They are exactly the same, except the missing blocking_timeout attribute.
> 
> 
> [sboisvert at GT480:Source]$ grep -A 10 "struct ustctl_consumer_channel_attr {" lttng-ust/include/lttng/ust-ctl.h
> struct ustctl_consumer_channel_attr {
> 	enum lttng_ust_chan_type type;
> 	uint64_t subbuf_size;			/* bytes */
> 	uint64_t num_subbuf;			/* power of 2 */
> 	int overwrite;				/* 1: overwrite, 0: discard */
> 	unsigned int switch_timer_interval;	/* usec */
> 	unsigned int read_timer_interval;	/* usec */
> 	enum lttng_ust_output output;		/* splice, mmap */
> 	uint32_t chan_id;			/* channel ID */
> 	unsigned char uuid[LTTNG_UST_UUID_LEN]; /* Trace session unique ID */
> } LTTNG_PACKED;
> 
> [sboisvert at GT480:Source]$ grep -A 11 "struct ustctl_consumer_channel_attr {" lttng-tools/src/bin/lttng-sessiond/lttng-ust-ctl.h
> struct ustctl_consumer_channel_attr {
> 	enum lttng_ust_chan_type type;
> 	uint64_t subbuf_size;			/* bytes */
> 	uint64_t num_subbuf;			/* power of 2 */
> 	int overwrite;				/* 1: overwrite, 0: discard */
> 	unsigned int switch_timer_interval;	/* usec */
> 	unsigned int read_timer_interval;	/* usec */
> 	enum lttng_ust_output output;		/* splice, mmap */
> 	uint32_t chan_id;			/* channel ID */
> 	unsigned char uuid[LTTNG_UST_UUID_LEN]; /* Trace session unique ID */
> 	int64_t blocking_timeout;			/* Blocking timeout (usec) */
> } LTTNG_PACKED;
> 
> [sboisvert at GT480:Source]$ diff -u <(grep -A 11 "struct ustctl_consumer_channel_attr {" lttng-tools/src/bin/lttng-sessiond/lttng-ust-ctl.h) <(grep -A 10 "struct ustctl_consumer_channel_attr {" lttng-ust/include/lttng/ust-ctl.h)
> --- /dev/fd/63	2019-05-10 12:32:23.562246820 -0400
> +++ /dev/fd/62	2019-05-10 12:32:23.562246820 -0400
> @@ -8,5 +8,4 @@
>  	enum lttng_ust_output output;		/* splice, mmap */
>  	uint32_t chan_id;			/* channel ID */
>  	unsigned char uuid[LTTNG_UST_UUID_LEN]; /* Trace session unique ID */
> -	int64_t blocking_timeout;			/* Blocking timeout (usec) */
>  } LTTNG_PACKED;
> 
>  
> My configure commands (followed by "make install"):
> 
> [sboisvert at GT480:userspace-rcu]$ ./configure --prefix=/home/sboisvert/open-source/lttng.org/Build/userspace-rcu/v0.11.0
> 
> [sboisvert at GT480:lttng-ust]$ ./configure --prefix=/home/sboisvert/open-source/lttng.org/Build/lttng-ust/v2.9.4 LDFLAGS=-L/home/sboisvert/open-source/lttng.org/Build/userspace-rcu/v0.11.0/lib
> 
> [sboisvert at GT480:lttng-tools]$ ./configure --prefix=/home/sboisvert/open-source/lttng.org/Build/lttng-tools/b14f53d4 LDFLAGS=-L/home/sboisvert/open-source/lttng.org/Build/lttng-ust/v2.9.4/lib CPPFLAGS=-I/home/sboisvert/open-source/lttng.org/Build/lttng-ust/v2.9.4/include
> 

This is probably an artefact but all your path have 2.9 in them. This work is
done against master of lttng-tools and lttng-ust.

Our CI does not indicate any failure for the master branches. [1]

[1] 

Cheers