[PATCH -mm] Taskstats fix the structure members alignment issue

Balbir Singh
2007-04-20T16:43:58Z

We broke the the alignment of members of taskstats to the 8 byte boundary
with the CSA patches. In the current kernel, the taskstats structure is
not suitable for use by 32 bit applications in a 64 bit kernel.

On x86_64

Offsets of taskstats' members (64 bit kernel, 64 bit application)

@taskstats'offsetof[@taskstats'indices] = (
0, # version
4, # ac_exitcode
8, # ac_flag
9, # ac_nice
16, # cpu_count
24, # cpu_delay_total
32, # blkio_count
40, # blkio_delay_total
48, # swapin_count
56, # swapin_delay_total
64, # cpu_run_real_total
72, # cpu_run_virtual_total
80, # ac_comm
112, # ac_sched
113, # ac_pad
116, # ac_uid
120, # ac_gid
124, # ac_pid
128, # ac_ppid
132, # ac_btime
136, # ac_etime
144, # ac_utime
152, # ac_stime
160, # ac_minflt
168, # ac_majflt
176, # coremem
184, # virtmem
192, # hiwater_rss
200, # hiwater_vm
208, # read_char
216, # write_char
224, # read_syscalls
232, # write_syscalls
240, # read_bytes
248, # write_bytes
256, # cancelled_write_bytes
);

Offsets of taskstats' members (64 bit kernel, 32 bit application)

@taskstats'offsetof[@taskstats'indices] = (
0, # version
4, # ac_exitcode
8, # ac_flag
9, # ac_nice
12, # cpu_count
20, # cpu_delay_total
28, # blkio_count
36, # blkio_delay_total
44, # swapin_count
52, # swapin_delay_total
60, # cpu_run_real_total
68, # cpu_run_virtual_total
76, # ac_comm
108, # ac_sched
109, # ac_pad
112, # ac_uid
116, # ac_gid
120, # ac_pid
124, # ac_ppid
128, # ac_btime
132, # ac_etime
140, # ac_utime
148, # ac_stime
156, # ac_minflt
164, # ac_majflt
172, # coremem
180, # virtmem
188, # hiwater_rss
196, # hiwater_vm
204, # read_char
212, # write_char
220, # read_syscalls
228, # write_syscalls
236, # read_bytes
244, # write_bytes
252, # cancelled_write_bytes
);

This is one way to solve the problem without re-arranging structure members is
to pack the structure. The patch adds an __attribute__((aligned(8))) to the
taskstats structure members so that 32 bit applications using taskstats
can work with a 64 bit kernel.

Using __attribute__((packed)) would break the 64 bit alignment of members.

The fix was tested on x86_64. After the fix, we got

Offsets of taskstats' members (64 bit kernel, 64 bit application)

@taskstats'offsetof[@taskstats'indices] = (
0, # version
4, # ac_exitcode
8, # ac_flag
9, # ac_nice
16, # cpu_count
24, # cpu_delay_total
32, # blkio_count
40, # blkio_delay_total
48, # swapin_count
56, # swapin_delay_total
64, # cpu_run_real_total
72, # cpu_run_virtual_total
80, # ac_comm
112, # ac_sched
113, # ac_pad
120, # ac_uid
124, # ac_gid
128, # ac_pid
132, # ac_ppid
136, # ac_btime
144, # ac_etime
152, # ac_utime
160, # ac_stime
168, # ac_minflt
176, # ac_majflt
184, # coremem
192, # virtmem
200, # hiwater_rss
208, # hiwater_vm
216, # read_char
224, # write_char
232, # read_syscalls
240, # write_syscalls
248, # read_bytes
256, # write_bytes
264, # cancelled_write_bytes
);

Offsets of taskstats' members (64 bit kernel, 32 bit application)

@taskstats'offsetof[@taskstats'indices] = (
0, # version
4, # ac_exitcode
8, # ac_flag
9, # ac_nice
16, # cpu_count
24, # cpu_delay_total
32, # blkio_count
40, # blkio_delay_total
48, # swapin_count
56, # swapin_delay_total
64, # cpu_run_real_total
72, # cpu_run_virtual_total
80, # ac_comm
112, # ac_sched
113, # ac_pad
120, # ac_uid
124, # ac_gid
128, # ac_pid
132, # ac_ppid
136, # ac_btime
144, # ac_etime
152, # ac_utime
160, # ac_stime
168, # ac_minflt
176, # ac_majflt
184, # coremem
192, # virtmem
200, # hiwater_rss
208, # hiwater_vm
216, # read_char
224, # write_char
232, # read_syscalls
240, # write_syscalls
248, # read_bytes
256, # write_bytes
264, # cancelled_write_bytes
);

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

include/linux/taskstats.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff -puN include/linux/taskstats.h~fix-taskstats-alignment include/linux/taskstats.h
--- linux-2.6.20/include/linux/taskstats.h~fix-taskstats-alignment 2007-04-19 12:28:25.000000000 +0530
+++ linux-2.6.20-balbir/include/linux/taskstats.h 2007-04-19 13:21:48.000000000 +0530
@@ -66,7 +66,7 @@ struct taskstats {
/* Delay waiting for cpu, while runnable
* count, delay_total NOT updated atomically
*/
- __u64 cpu_count;
+ __u64 cpu_count __attribute__((aligned(8)));
__u64 cpu_delay_total;

/* Following four fields atomically updated using task->delays->lock */
@@ -101,14 +101,17 @@ struct taskstats {

/* Basic Accounting Fields start */
char ac_comm[TS_COMM_LEN]; /* Command name */
- __u8 ac_sched; /* Scheduling discipline */
+ __u8 ac_sched __attribute__((aligned(8)));
+ /* Scheduling discipline */
__u8 ac_pad[3];
- __u32 ac_uid; /* User ID */
+ __u32 ac_uid __attribute__((aligned(8)));
+ /* User ID */
__u32 ac_gid; /* Group ID */
__u32 ac_pid; /* Process ID */
__u32 ac_ppid; /* Parent process ID */
__u32 ac_btime; /* Begin time [sec since 1970] */
- __u64 ac_etime; /* Elapsed time [usec] */
+ __u64 ac_etime __attribute__((aligned(8)));
+ /* Elapsed time [usec] */
__u64 ac_utime; /* User CPU time [usec] */
__u64 ac_stime; /* SYstem CPU time [usec] */
__u64 ac_minflt; /* Minor Page Fault Count */
_

--
Warm Regards,