diff options
author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-03-22 17:30:58 -0400 |
---|---|---|
committer | Sasha Levin <sasha.levin@oracle.com> | 2016-04-18 08:49:38 -0400 |
commit | 51d109b05dea76910c6b5c95908e9e334888f46f (patch) | |
tree | ae2c325cf72e8134319757cb376707b26fa8c3c7 /fs | |
parent | 241a9a816bc95d7bbc7c422c60e880491a59ac1b (diff) |
tracing: Fix trace_printk() to print when not using bprintk()
[ Upstream commit 3debb0a9ddb16526de8b456491b7db60114f7b5e ]
The trace_printk() code will allocate extra buffers if the compile detects
that a trace_printk() is used. To do this, the format of the trace_printk()
is saved to the __trace_printk_fmt section, and if that section is bigger
than zero, the buffers are allocated (along with a message that this has
happened).
If trace_printk() uses a format that is not a constant, and thus something
not guaranteed to be around when the print happens, the compiler optimizes
the fmt out, as it is not used, and the __trace_printk_fmt section is not
filled. This means the kernel will not allocate the special buffers needed
for the trace_printk() and the trace_printk() will not write anything to the
tracing buffer.
Adding a "__used" to the variable in the __trace_printk_fmt section will
keep it around, even though it is set to NULL. This will keep the string
from being printed in the debugfs/tracing/printk_formats section as it is
not needed.
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()"
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'fs')
0 files changed, 0 insertions, 0 deletions