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Commit 7a2a3071 authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

liblog: resolve deadlocks 

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. Block signals while we
are locked. Separate out timestamp lock from is loggable lock to
reduce contention situations. Provide a best-guess response if
lock would fail in timestamp path.

Bug: 25563384
Change-Id: I6dccd6b99ebace1c473c03a785a35c63ed5c6a8a
parent 8ce943b3

include/log/log.h

+6 −1
Original line number Diff line number Diff line
@@ -616,7 +616,12 @@ typedef enum log_id { 
 * Use the per-tag properties "log.tag.<tagname>" to generate a runtime

 * result of non-zero to expose a log.

 */

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

/* default prio ANDROID_LOG_VERBOSE to ANDROID_LOG_FATAL if no property */

#define ANDROID_LOGGABLE_FLAG_DEFAULT_MASK      0x000F

/* Save 2 syscalls if caller guarantees to never call within signal handler */

#define ANDROID_LOGGABLE_FLAG_NOT_WITHIN_SIGNAL 0x8000



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



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

                              uint32_t dataLen);

liblog/fake_log_device.c

+30 −11
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 
#include <ctype.h>

#include <errno.h>

#include <fcntl.h>

#include <signal.h>

#include <stdlib.h>

#include <string.h>
@@ -97,18 +98,33 @@ typedef struct LogState { 
 */

static pthread_mutex_t fakeLogDeviceLock = PTHREAD_MUTEX_INITIALIZER;



static void lock()

static void lock(sigset_t *sigflags)

{

    /*

     * 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.

     */

    sigset_t all;



    sigfillset(&all);

    pthread_sigmask(SIG_BLOCK, &all, sigflags);

    pthread_mutex_lock(&fakeLogDeviceLock);

}



static void unlock()

static void unlock(sigset_t *sigflags)

{

    pthread_mutex_unlock(&fakeLogDeviceLock);

    pthread_sigmask(SIG_UNBLOCK, sigflags, NULL);

}



#define DECLARE_SIGSET(name) sigset_t name



#else   // !defined(_WIN32)

#define lock() ((void)0)

#define unlock() ((void)0)



#define lock(sigflags) ((void)0)

#define unlock(sigflags) ((void)0)

#define DECLARE_SIGSET(name)



#endif  // !defined(_WIN32)
@@ -154,8 +170,9 @@ static LogState *fdToLogState(int fd) 
static void deleteFakeFd(int fd)

{

    LogState *ls;

    DECLARE_SIGSET(sigflags);



    lock();

    lock(&sigflags);



    ls = fdToLogState(fd);

    if (ls != NULL) {
@@ -164,7 +181,7 @@ static void deleteFakeFd(int fd) 
        free(ls);

    }



    unlock();

    unlock(&sigflags);

}



/*
@@ -548,12 +565,13 @@ static void showLog(LogState *state, 
static ssize_t logWritev(int fd, const struct iovec* vector, int count)

{

    LogState* state;

    DECLARE_SIGSET(sigflags);



    /* Make sure that no-one frees the LogState while we're using it.

     * Also guarantees that only one thread is in showLog() at a given

     * time (if it matters).

     */

    lock();

    lock(&sigflags);



    state = fdToLogState(fd);

    if (state == NULL) {
@@ -598,10 +616,10 @@ static ssize_t logWritev(int fd, const struct iovec* vector, int count) 
    }



bail:

    unlock();

    unlock(&sigflags);

    return vector[0].iov_len + vector[1].iov_len + vector[2].iov_len;

error:

    unlock();

    unlock(&sigflags);

    return -1;

}
@@ -621,8 +639,9 @@ static int logOpen(const char* pathName, int flags __unused) 
{

    LogState *logState;

    int fd = -1;

    DECLARE_SIGSET(sigflags);



    lock();

    lock(&sigflags);



    logState = createLogState();

    if (logState != NULL) {
@@ -632,7 +651,7 @@ static int logOpen(const char* pathName, int flags __unused) 
        errno = ENFILE;

    }



    unlock();

    unlock(&sigflags);



    return fd;

}

liblog/log_is_loggable.c

+57 −21
Original line number Diff line number Diff line
@@ -16,12 +16,39 @@ 


#include <ctype.h>

#include <pthread.h>

#include <signal.h>

#include <stdlib.h>

#include <string.h>

#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_

#include <sys/_system_properties.h>



#include <android/log.h>

#include <log/log.h>



static pthread_mutex_t lock_loggable = PTHREAD_MUTEX_INITIALIZER;



static void lock(sigset_t *sigflags)

{

    /*

     * 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.

     */

    if (sigflags) {

        sigset_t all;



        sigfillset(&all);

        pthread_sigmask(SIG_BLOCK, &all, sigflags);

    }

    pthread_mutex_lock(&lock_loggable);

}



static void unlock(sigset_t *sigflags)

{

    pthread_mutex_unlock(&lock_loggable);

    if (sigflags) {

        pthread_sigmask(SIG_UNBLOCK, sigflags, NULL);

    }

}



struct cache {

    const prop_info *pinfo;
@@ -49,9 +76,7 @@ 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 flag)

{

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

    static const char log_namespace[] = "persist.log.tag.";
@@ -83,10 +108,11 @@ static int __android_log_level(const char *tag, int def) 
        { NULL, -1, 0 },

        { NULL, -1, 0 }

    };

    sigset_t sigflags;



    strcpy(key, log_namespace);



    pthread_mutex_lock(&lock);

    lock((flag & ANDROID_LOGGABLE_FLAG_NOT_WITHIN_SIGNAL) ? NULL : &sigflags);



    current_global_serial = __system_property_area_serial();
@@ -156,7 +182,7 @@ static int __android_log_level(const char *tag, int def) 


    global_serial = current_global_serial;



    pthread_mutex_unlock(&lock);

    unlock((flag & ANDROID_LOGGABLE_FLAG_NOT_WITHIN_SIGNAL) ? NULL : &sigflags);



    switch (toupper(c)) {

    case 'V': return ANDROID_LOG_VERBOSE;
@@ -168,26 +194,35 @@ 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 flag & ANDROID_LOGGABLE_FLAG_DEFAULT_MASK;

}



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

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

{

    int logLevel = __android_log_level(tag, def);

    int logLevel = __android_log_level(tag, flag);

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

}



/*

 * Timestamp state generally remains constant, since a change is

 * rare, we can accept a trylock failure gracefully.

 */

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 +232,8 @@ 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

+42 −18
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <fcntl.h>

#if !defined(_WIN32)

#include <pthread.h>

#include <signal.h>

#endif

#include <stdarg.h>

#include <stdatomic.h>
@@ -54,14 +55,43 @@ 


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(sigset_t *sigflags)

{

    /*

     * 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.

     */

    sigset_t all;



    sigfillset(&all);

    pthread_sigmask(SIG_BLOCK, &all, sigflags);

    pthread_mutex_lock(&log_init_lock);

}



static void unlock(sigset_t *sigflags)

{

    pthread_mutex_unlock(&log_init_lock);

    pthread_sigmask(SIG_UNBLOCK, sigflags, NULL);

}



#define DECLARE_SIGSET(name) sigset_t name



#else   /* !defined(_WIN32) */



#define lock(sigflags) ((void)0)

#define unlock(sigflags) ((void)0)

#define DECLARE_SIGSET(name)



#endif  /* !defined(_WIN32) */



#if FAKE_LOG_DEVICE

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

#else
@@ -275,17 +305,15 @@ static int __write_to_log_daemon(log_id_t log_id, struct iovec *vec, size_t nr) 
     */

    ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, i - 1));

    if (ret < 0) {

        DECLARE_SIGSET(sigflags);



        ret = -errno;

        if (ret == -ENOTCONN) {

#if !defined(_WIN32)

            pthread_mutex_lock(&log_init_lock);

#endif

            lock(&sigflags);

            close(logd_fd);

            logd_fd = -1;

            ret = __write_to_log_initialize();

#if !defined(_WIN32)

            pthread_mutex_unlock(&log_init_lock);

#endif

            unlock(&sigflags);



            if (ret < 0) {

                return ret;
@@ -329,18 +357,16 @@ 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

    DECLARE_SIGSET(sigflags);



    lock(&sigflags);



    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(&sigflags);

#if (FAKE_LOG_DEVICE == 0)

            if (pstore_fd >= 0) {

                __write_to_log_daemon(log_id, vec, nr);
@@ -352,9 +378,7 @@ 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(&sigflags);



    return write_to_log(log_id, vec, nr);

}

logd/LogBuffer.cpp

+3 −1
Original line number Diff line number Diff line
@@ -191,7 +191,9 @@ int LogBuffer::log(log_id_t log_id, log_time realtime, 
        prio = *msg;

        tag = msg + 1;

    }

    if (!__android_log_is_loggable(prio, tag, ANDROID_LOG_VERBOSE)) {

    if (!__android_log_is_loggable(prio, tag,

                                   ANDROID_LOG_VERBOSE |

                                   ANDROID_LOGGABLE_FLAG_NOT_WITHIN_SIGNAL)) {

        // Log traffic received to total

        pthread_mutex_lock(&mLogElementsLock);

        stats.add(elem);