Current snapshot implementation swaps two ring_buffers even though their
sizes are different from each other, that can cause an inconsistency
between the contents of buffer_size_kb file and the current buffer size.
For example:
# cat buffer_size_kb
7 (expanded: 1408)
# echo 1 > events/enable
# grep bytes per_cpu/cpu0/stats
bytes: 1441020
# echo 1 > snapshot // current:1408, spare:1408
# echo 123 > buffer_size_kb // current:123, spare:1408
# echo 1 > snapshot // current:1408, spare:123
# grep bytes per_cpu/cpu0/stats
bytes: 1443700
# cat buffer_size_kb
123 // != current:1408
And also, a similar per-cpu case hits the following WARNING:
Reproducer:
# echo 1 > per_cpu/cpu0/snapshot
# echo 123 > buffer_size_kb
# echo 1 > per_cpu/cpu0/snapshot
WARNING:
WARNING: CPU: 0 PID: 1946 at kernel/trace/trace.c:1607 update_max_tr_single.part.0+0x2b8/0x380
Modules linked in:
CPU: 0 PID: 1946 Comm: bash Not tainted 5.2.0-rc6 #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
RIP: 0010:update_max_tr_single.part.0+0x2b8/0x380
Code: ff e8 dc da f9 ff 0f 0b e9 88 fe ff ff e8 d0 da f9 ff 44 89 ee bf f5 ff ff ff e8 33 dc f9 ff 41 83 fd f5 74 96 e8 b8 da f9 ff <0f> 0b eb 8d e8 af da f9 ff 0f 0b e9 bf fd ff ff e8 a3 da f9 ff 48
RSP: 0018:ffff888063e4fca0 EFLAGS: 00010093
RAX: ffff888066214380 RBX: ffffffff99850fe0 RCX: ffffffff964298a8
RDX: 0000000000000000 RSI: 00000000fffffff5 RDI: 0000000000000005
RBP: 1ffff1100c7c9f96 R08: ffff888066214380 R09: ffffed100c7c9f9b
R10: ffffed100c7c9f9a R11: 0000000000000003 R12: 0000000000000000
R13: 00000000ffffffea R14: ffff888066214380 R15: ffffffff99851060
FS: 00007f9f8173c700(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000714dc0 CR3: 0000000066fa6000 CR4: 00000000000006f0
Call Trace:
? trace_array_printk_buf+0x140/0x140
? __mutex_lock_slowpath+0x10/0x10
tracing_snapshot_write+0x4c8/0x7f0
? trace_printk_init_buffers+0x60/0x60
? selinux_file_permission+0x3b/0x540
? tracer_preempt_off+0x38/0x506
? trace_printk_init_buffers+0x60/0x60
__vfs_write+0x81/0x100
vfs_write+0x1e1/0x560
ksys_write+0x126/0x250
? __ia32_sys_read+0xb0/0xb0
? do_syscall_64+0x1f/0x390
do_syscall_64+0xc1/0x390
entry_SYSCALL_64_after_hwframe+0x49/0xbe
This patch adds resize_buffer_duplicate_size() to check if there is a
difference between current/spare buffer sizes and resize a spare buffer
if necessary.
Signed-off-by: Eiichi Tsukata <[email protected]>
---
kernel/trace/trace.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 83e08b78dbee..3edd4c1b96be 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6719,11 +6719,13 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
break;
}
#endif
- if (!tr->allocated_snapshot) {
+ if (tr->allocated_snapshot)
+ ret = resize_buffer_duplicate_size(&tr->max_buffer,
+ &tr->trace_buffer, iter->cpu_file);
+ else
ret = tracing_alloc_snapshot_instance(tr);
- if (ret < 0)
- break;
- }
+ if (ret < 0)
+ break;
local_irq_disable();
/* Now, we're going to swap */
if (iter->cpu_file == RING_BUFFER_ALL_CPUS)
--
2.21.0
On Tue, 25 Jun 2019 10:29:10 +0900
Eiichi Tsukata <[email protected]> wrote:
> Current snapshot implementation swaps two ring_buffers even though their
> sizes are different from each other, that can cause an inconsistency
> between the contents of buffer_size_kb file and the current buffer size.
>
> For example:
>
> # cat buffer_size_kb
> 7 (expanded: 1408)
> # echo 1 > events/enable
> # grep bytes per_cpu/cpu0/stats
> bytes: 1441020
> # echo 1 > snapshot // current:1408, spare:1408
> # echo 123 > buffer_size_kb // current:123, spare:1408
> # echo 1 > snapshot // current:1408, spare:123
> # grep bytes per_cpu/cpu0/stats
> bytes: 1443700
> # cat buffer_size_kb
> 123 // != current:1408
>
> And also, a similar per-cpu case hits the following WARNING:
>
> Reproducer:
>
> # echo 1 > per_cpu/cpu0/snapshot
> # echo 123 > buffer_size_kb
> # echo 1 > per_cpu/cpu0/snapshot
>
> WARNING:
>
> WARNING: CPU: 0 PID: 1946 at kernel/trace/trace.c:1607 update_max_tr_single.part.0+0x2b8/0x380
> Modules linked in:
> CPU: 0 PID: 1946 Comm: bash Not tainted 5.2.0-rc6 #20
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
> RIP: 0010:update_max_tr_single.part.0+0x2b8/0x380
> Code: ff e8 dc da f9 ff 0f 0b e9 88 fe ff ff e8 d0 da f9 ff 44 89 ee bf f5 ff ff ff e8 33 dc f9 ff 41 83 fd f5 74 96 e8 b8 da f9 ff <0f> 0b eb 8d e8 af da f9 ff 0f 0b e9 bf fd ff ff e8 a3 da f9 ff 48
> RSP: 0018:ffff888063e4fca0 EFLAGS: 00010093
> RAX: ffff888066214380 RBX: ffffffff99850fe0 RCX: ffffffff964298a8
> RDX: 0000000000000000 RSI: 00000000fffffff5 RDI: 0000000000000005
> RBP: 1ffff1100c7c9f96 R08: ffff888066214380 R09: ffffed100c7c9f9b
> R10: ffffed100c7c9f9a R11: 0000000000000003 R12: 0000000000000000
> R13: 00000000ffffffea R14: ffff888066214380 R15: ffffffff99851060
> FS: 00007f9f8173c700(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000714dc0 CR3: 0000000066fa6000 CR4: 00000000000006f0
> Call Trace:
> ? trace_array_printk_buf+0x140/0x140
> ? __mutex_lock_slowpath+0x10/0x10
> tracing_snapshot_write+0x4c8/0x7f0
> ? trace_printk_init_buffers+0x60/0x60
> ? selinux_file_permission+0x3b/0x540
> ? tracer_preempt_off+0x38/0x506
> ? trace_printk_init_buffers+0x60/0x60
> __vfs_write+0x81/0x100
> vfs_write+0x1e1/0x560
> ksys_write+0x126/0x250
> ? __ia32_sys_read+0xb0/0xb0
> ? do_syscall_64+0x1f/0x390
> do_syscall_64+0xc1/0x390
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> This patch adds resize_buffer_duplicate_size() to check if there is a
> difference between current/spare buffer sizes and resize a spare buffer
> if necessary.
>
> Signed-off-by: Eiichi Tsukata <[email protected]>
>
Applied, thanks Eiichi!
-- Steve