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Commit f280b020 authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

liblog: resolve deadlocks (part deux) 



(cherry pick from commit 2d2e0a5c)

Although ever present, an increased regression introduced with
commit b6bee331 (liblog: logd:
support logd.timestamp = monotonic).

A signal handler can interrupt in locked context, if log is written
in the signal handler, we are in deadlock. To reduce the contention
and chances for this problem separate out timestamp lock from is
loggable lock to reduce contention situations. Provide a best-guess
response if lock would fail in timestamp path.

Use a common lock() inline within each module, with a comment speaking
to the issues surrounding calling a function that has a mutex within
a signal handler.

ToDo: Hold off signals temporarily in mainline, restart when unblock.
      Can not use pthread_sigmask(SIG_BLOCK,,) as it breaks AtCmd.

Signed-off-by: default avatarMark Salyzyn <salyzyn@google.com>
Bug: 25563384
Change-Id: I47e2c87c988c3e359eb9eef129c6a3a08e9eedef
parent 67114e63

include/log/log.h

+4 −2
Original line number Diff line number Diff line
@@ -614,9 +614,11 @@ typedef enum log_id { 


/*

 * Use the per-tag properties "log.tag.<tagname>" to generate a runtime

 * result of non-zero to expose a log.

 * result of non-zero to expose a log. prio is ANDROID_LOG_VERBOSE to

 * ANDROID_LOG_FATAL. default_prio if no property. Undefined behavior if

 * any other value.

 */

int __android_log_is_loggable(int prio, const char *tag, int def);

int __android_log_is_loggable(int prio, const char *tag, int default_prio);



int __android_log_error_write(int tag, const char *subTag, int32_t uid, const char *data,

                              uint32_t dataLen);

liblog/fake_log_device.c

+7 −0
Original line number Diff line number Diff line
@@ -99,6 +99,10 @@ static pthread_mutex_t fakeLogDeviceLock = PTHREAD_MUTEX_INITIALIZER; 


static void lock()

{

    /*

     * If we trigger a signal handler in the middle of locked activity and the

     * signal handler logs a message, we could get into a deadlock state.

     */

    pthread_mutex_lock(&fakeLogDeviceLock);

}
@@ -106,9 +110,12 @@ static void unlock() 
{

    pthread_mutex_unlock(&fakeLogDeviceLock);

}



#else   // !defined(_WIN32)



#define lock() ((void)0)

#define unlock() ((void)0)



#endif  // !defined(_WIN32)

liblog/log_is_loggable.c

+46 −21
Original line number Diff line number Diff line
@@ -23,6 +23,22 @@ 


#include <android/log.h>



static pthread_mutex_t lock_loggable = PTHREAD_MUTEX_INITIALIZER;



static void lock()

{

    /*

     * If we trigger a signal handler in the middle of locked activity and the

     * signal handler logs a message, we could get into a deadlock state.

     */

    pthread_mutex_lock(&lock_loggable);

}



static void unlock()

{

    pthread_mutex_unlock(&lock_loggable);

}



struct cache {

    const prop_info *pinfo;

    uint32_t serial;
@@ -49,9 +65,7 @@ static void refresh_cache(struct cache *cache, const char *key) 
    cache->c = buf[0];

}



static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;



static int __android_log_level(const char *tag, int def)

static int __android_log_level(const char *tag, int default_prio)

{

    /* sizeof() is used on this array below */

    static const char log_namespace[] = "persist.log.tag.";
@@ -86,7 +100,7 @@ static int __android_log_level(const char *tag, int def) 


    strcpy(key, log_namespace);



    pthread_mutex_lock(&lock);

    lock();



    current_global_serial = __system_property_area_serial();
@@ -156,7 +170,7 @@ static int __android_log_level(const char *tag, int def) 


    global_serial = current_global_serial;



    pthread_mutex_unlock(&lock);

    unlock();



    switch (toupper(c)) {

    case 'V': return ANDROID_LOG_VERBOSE;
@@ -168,26 +182,36 @@ static int __android_log_level(const char *tag, int def) 
    case 'A': return ANDROID_LOG_FATAL;

    case 'S': return -1; /* ANDROID_LOG_SUPPRESS */

    }

    return def;

    return default_prio;

}



int __android_log_is_loggable(int prio, const char *tag, int def)

int __android_log_is_loggable(int prio, const char *tag, int default_prio)

{

    int logLevel = __android_log_level(tag, def);

    int logLevel = __android_log_level(tag, default_prio);

    return logLevel >= 0 && prio >= logLevel;

}



/*

 * Timestamp state generally remains constant, since a change is

 * rare, we can accept a trylock failure gracefully. Use a separate

 * lock from is_loggable to keep contention down b/25563384.

 */

static pthread_mutex_t lock_timestamp = PTHREAD_MUTEX_INITIALIZER;



char android_log_timestamp()

{

    static struct cache r_time_cache = { NULL, -1, 0 };

    static struct cache p_time_cache = { NULL, -1, 0 };

    static uint32_t serial;

    uint32_t current_serial;

    char retval;



    pthread_mutex_lock(&lock);



    current_serial = __system_property_area_serial();

    if (pthread_mutex_trylock(&lock_timestamp)) {

        /* We are willing to accept some race in this context */

        if (!(retval = p_time_cache.c)) {

            retval = r_time_cache.c;

        }

    } else {

        static uint32_t serial;

        uint32_t current_serial = __system_property_area_serial();

        if (current_serial != serial) {

            refresh_cache(&r_time_cache, "ro.logd.timestamp");

            refresh_cache(&p_time_cache, "persist.logd.timestamp");
@@ -197,7 +221,8 @@ char android_log_timestamp() 
            retval = r_time_cache.c;

        }



    pthread_mutex_unlock(&lock);

        pthread_mutex_unlock(&lock_timestamp);

    }



    return tolower(retval ?: 'r');

}

liblog/logd_write.c

+29 −18
Original line number Diff line number Diff line
@@ -54,14 +54,35 @@ 


static int __write_to_log_init(log_id_t, struct iovec *vec, size_t nr);

static int (*write_to_log)(log_id_t, struct iovec *vec, size_t nr) = __write_to_log_init;

#if !defined(_WIN32)

static pthread_mutex_t log_init_lock = PTHREAD_MUTEX_INITIALIZER;

#endif



#ifndef __unused

#define __unused  __attribute__((__unused__))

#endif



#if !defined(_WIN32)

static pthread_mutex_t log_init_lock = PTHREAD_MUTEX_INITIALIZER;



static void lock()

{

    /*

     * If we trigger a signal handler in the middle of locked activity and the

     * signal handler logs a message, we could get into a deadlock state.

     */

    pthread_mutex_lock(&log_init_lock);

}



static void unlock()

{

    pthread_mutex_unlock(&log_init_lock);

}



#else   /* !defined(_WIN32) */



#define lock() ((void)0)

#define unlock() ((void)0)



#endif  /* !defined(_WIN32) */



#if FAKE_LOG_DEVICE

static int log_fds[(int)LOG_ID_MAX] = { -1, -1, -1, -1, -1 };

#else
@@ -277,15 +298,11 @@ static int __write_to_log_daemon(log_id_t log_id, struct iovec *vec, size_t nr) 
    if (ret < 0) {

        ret = -errno;

        if (ret == -ENOTCONN) {

#if !defined(_WIN32)

            pthread_mutex_lock(&log_init_lock);

#endif

            lock();

            close(logd_fd);

            logd_fd = -1;

            ret = __write_to_log_initialize();

#if !defined(_WIN32)

            pthread_mutex_unlock(&log_init_lock);

#endif

            unlock();



            if (ret < 0) {

                return ret;
@@ -329,18 +346,14 @@ const char *android_log_id_to_name(log_id_t log_id) 


static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr)

{

#if !defined(_WIN32)

    pthread_mutex_lock(&log_init_lock);

#endif

    lock();



    if (write_to_log == __write_to_log_init) {

        int ret;



        ret = __write_to_log_initialize();

        if (ret < 0) {

#if !defined(_WIN32)

            pthread_mutex_unlock(&log_init_lock);

#endif

            unlock();

#if (FAKE_LOG_DEVICE == 0)

            if (pstore_fd >= 0) {

                __write_to_log_daemon(log_id, vec, nr);
@@ -352,9 +365,7 @@ static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr) 
        write_to_log = __write_to_log_daemon;

    }



#if !defined(_WIN32)

    pthread_mutex_unlock(&log_init_lock);

#endif

    unlock();



    return write_to_log(log_id, vec, nr);

}