[ovs-dev] [PATCHv2] fatal-signal: Fix clang error due to lock.

Ilya Maximets i.maximets at ovn.org
Tue Mar 24 14:27:18 UTC 2020


On 3/24/20 3:17 PM, William Tu wrote:
> Due to not acquiring lock, clang reports:
>   lib/vlog.c:618:12: error: reading variable 'log_fd' requires holding mutex
>   'log_file_mutex' [-Werror,-Wthread-safety-analysis]
>   return log_fd;
> 
> The patch fixes it by creating a function in vlog.c to write
> directly to log file unsafely.
> 
> Tested-at: https://travis-ci.org/github/williamtu/ovs-travis/builds/666165883
> Fixes: ecd4a8fcdff2 ("fatal-signal: Log backtrace when no monitor daemon.")
> Suggested-by: Ilya Maximets <i.maximets at ovn.org>
> Signed-off-by: William Tu <u9012063 at gmail.com>
> ---
>  include/openvswitch/vlog.h |  4 ++--
>  lib/fatal-signal.c         |  8 ++------
>  lib/vlog.c                 | 15 ++++++++++++---
>  3 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/include/openvswitch/vlog.h b/include/openvswitch/vlog.h
> index 476bf3d6d5b4..886fce5e0fd5 100644
> --- a/include/openvswitch/vlog.h
> +++ b/include/openvswitch/vlog.h
> @@ -143,8 +143,8 @@ void vlog_set_syslog_method(const char *method);
>  /* Configure syslog target. */
>  void vlog_set_syslog_target(const char *target);
>  
> -/* Return the log_fd. */
> -int vlog_get_fd(void);
> +/* Write directly to log file. */
> +void vlog_direct_write_to_log_file_unsafe(const char *s);
>  
>  /* Initialization. */
>  void vlog_init(void);
> diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c
> index 4965c1ae82c0..51cf628d994e 100644
> --- a/lib/fatal-signal.c
> +++ b/lib/fatal-signal.c
> @@ -197,11 +197,7 @@ send_backtrace_to_monitor(void) {
>           */
>          char str[] = "SIGSEGV detected, backtrace:\n";
>  
> -        if (vlog_get_fd() < 0) {
> -            return;
> -        }
> -
> -        ignore(write(vlog_get_fd(), str, strlen(str)));
> +        vlog_direct_write_to_log_file_unsafe(str);
>  
>          for (int i = 0; i < dep; i++) {
>              char line[64];
> @@ -210,7 +206,7 @@ send_backtrace_to_monitor(void) {
>                       unw_bt[i].ip,
>                       unw_bt[i].func,
>                       unw_bt[i].offset);
> -            ignore(write(vlog_get_fd(), line, strlen(line)));
> +            vlog_direct_write_to_log_file_unsafe(line);
>          }
>      }
>  }
> diff --git a/lib/vlog.c b/lib/vlog.c
> index 502b33fc831e..6d17d4837e9c 100644
> --- a/lib/vlog.c
> +++ b/lib/vlog.c
> @@ -612,10 +612,19 @@ vlog_set_syslog_target(const char *target)
>      ovs_rwlock_unlock(&pattern_rwlock);
>  }
>  
> -int
> -vlog_get_fd(void)
> +/*
> + * This function writes directly to log file without using async writer or
> + * taking a lock.  Caller must hold 'log_file_mutex' or be sure that it's
> + * not necessary.  Could be used in exceptional cases like dumping of backtrace
> + * on fatal signals.
> + */
> +void
> +vlog_direct_write_to_log_file_unsafe(const char *s)
> +    OVS_NO_THREAD_SAFETY_ANALYSIS
>  {
> -    return log_fd;
> +    if (log_fd >= 0) {
> +        ignore(write(log_fd, s, strlen(s)));
> +    }
>  }
>  
>  /* Returns 'false' if 'facility' is not a valid string. If 'facility'
> 

So, does this work?
I mean, last time you said that this exact version of code doesn't print anything.

Best regards, Ilya Maximets. 


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