nrf_log fixes in SDK14.1.0

[Keton]

I've noticed following line in SDK14.1 release notes:

`

• Fixed a bug where nrf_log could crash when heavily loaded. `

I'm using SDK13.1 in my current project and I'm experiencing nrf_log related crashes under load as described here.

Please elaborate on what exactly was fixed and if it's related to problems I'm experiencing. Also if possible please provide some pointers on how to backport this fix into SDK13.1. Unfortunately I can't upgrade to SDK14.1 at this time.

[Krzysztof Chruscinski]

Hi,

you can try to find function cont_buf_prealloc in nrf_log_frontend.c and update following code:

uint32_t available_words = (m_log_data.mask + 1) -
                           (m_log_data.wr_idx & m_log_data.mask);

should be changed to:

uint32_t available_words = (m_log_data.mask + 1) -
                            (m_log_data.wr_idx - m_log_data.rd_idx);

That should help.

UPDATE Actually, the fix provided was not good and there was still a bug in SDK 14.2.0 in that function. Here is the updated version the function:

static inline uint32_t * cont_buf_prealloc(uint32_t len32,
                                       uint32_t * p_offset,
                                       uint32_t * p_wr_idx){
uint32_t * p_buf = NULL;

len32 += PUSHED_HEADER_SIZE; // Increment because 32bit header is needed to be stored.

CRITICAL_REGION_ENTER();
*p_wr_idx = m_log_data.wr_idx;
uint32_t available_words = (m_log_data.mask + 1) -
                            (m_log_data.wr_idx - m_log_data.rd_idx);
uint32_t cont_words =  (m_log_data.mask + 1) - (m_log_data.wr_idx & m_log_data.mask);

//available space is continuous
uint32_t curr_pos_available = (available_words <= cont_words) ? available_words : cont_words;
uint32_t start_pos_available = (available_words <= cont_words) ? 0 : (available_words - cont_words);
if (len32 <= curr_pos_available)
{
    // buffer will fit as is
    p_buf              = &m_log_data.buffer[(m_log_data.wr_idx + 1) & m_log_data.mask];
    m_log_data.wr_idx += len32;
    *p_offset          = 0;
}
else if (len32 <= start_pos_available)
{
    // wraping to the begining of the buffer
    m_log_data.wr_idx += (len32 + cont_words);
    *p_offset          = cont_words;
    p_buf              = m_log_data.buffer;
}

CRITICAL_REGION_EXIT();

return p_buf;}

[Keton]

thanks, it solved the problem for test case I've linked but still I'm able to crash MCU by doing bunch of: NRF_LOG_RAW_DEBUG("%s\r\n",nrf_log_push(str)); where str is: char str[150]. When I'm using SEGGER_RTT_Write instead of nrf_log it doesn't crash so it's most likely another memory access issue in nrf_log.

[Keton]

Any updates on this? I have a project where I have to use deffered logging due to timing constraints and NRF_LOG hardfaults every time.

[Keton]

could you please provide either whole body of cont_buf_prealloc() or git patch? I'm not sure what to do with the rest of the critical section.

[Keton]

SDK 13.1 nrf_log implementation has no definition of PUSHED_HEADER_SIZE. Can I assume that it's equal to 1 word as per comment on line 438 of nrf_log_internal.h in SDK14.2?

[Krzysztof Chruscinski]

yes, it is 1 word.