Re: m_get_tag returns same tag address when called multiple times

[Gleb Smirnoff]

On Wed, May 14, 2014 at 06:54:01AM +, Sreenivasa Honnur wrote:
S Hi,
S In FreeBSd-11 Current i am seeing that m_tag_get() returns same tag address 
for two subsequent calls, and m_tag_find() results in panic with below stack 
trace. Anything wrong here?

Difficult to believe that. Can you provide more code or even
better a test case that I can run?

Are you sure that we are speaking of m_tag_get(), not about
pf_get_mtag()?

-- 
Totus tuus, Glebius.
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m_get_tag returns same tag address when called multiple times

[Sreenivasa Honnur]

Hi,
In FreeBSd-11 Current i am seeing that m_tag_get() returns same tag address for 
two subsequent calls, and m_tag_find() results in panic with below stack trace. 
Anything wrong here?

Fatal trap 9: general protection fault while in kernel mode
cpuid = 4; apic id = 04
instruction pointer = 0x20:0x80959ff0
stack pointer   = 0x28:0xfe01acfa09a0
frame pointer   = 0x28:0xfe01acfa09d0
code segment= base 0x0, limit 0xf, type 0x1b
= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags= interrupt enabled, resume, IOPL = 0
current process = 12 (irq277: t5nex0:0,5)
[ thread pid 12 tid 100128 ]
Stopped at  m_tag_locate+0x40:  cmpl%ebx,0xc(%rcx)

Here is the calling sequence;

1. get_mbuf_mtag: m:0xf8005b3e4c00 mtag:0xf8002c47d180

2. get_mbuf_mtag: m:0xf8005b3e5000 mtag:0xf8002c47d180

3. find_mbuf_mtag(0xf8005b3e4c00) results in above trace.

Note that the same code works fine in FBSD-9.1.

struct my_mbuf_cb * get_mbuf_mtag(struct mbuf *m)
{
struct m_tag*mtag;

mtag = m_tag_get(PACKET_TAG_PF, sizeof(struct my_mbuf_cb), M_NOWAIT);
if (mtag == NULL) {
os_log_info(Error allocating mtag\n,);
return (NULL);
}
bzero(mtag + 1, sizeof(struct my_mbuf_cb));
m_tag_prepend(m, mtag);
 
return ((struct my_mbuf_cb *)(mtag + 1));
}

static struct my_mbuf_cb * find_mbuf_mtag(struct mbuf *m)
{
struct m_tag*mtag;

if ((mtag = m_tag_find(m, PACKET_TAG_PF, NULL)) == NULL)
return (NULL);

return ((struct my_mbuf_cb *)(mtag + 1));
}

Thanks
Sreenivas
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