[Bug 50981] New: ext4 : DATA CORRUPTION read and write on same 4096 page range

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https://bugzilla.kernel.org/show_bug.cgi?id=50981

           Summary: ext4 : DATA CORRUPTION read and write on same 4096
                    page  range
           Product: File System
           Version: 2.5
    Kernel Version: 2.6.32 Red Hat Enterprise Linux Workstation release
                    6.2 (Santiago)
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: ext4
        AssignedTo: fs_ext4@kernel-bugs.osdl.org
        ReportedBy: meetmehiro@gmail.com
        Regression: No


Kernal version and Red hat

2.6.32 , Red Hat Enterprise Linux Workstation release 6.2 (Santiago)


I have one scientific application, that is running on ext4 , after three to
fours days, I have started to seen that data is not correct.. then i tried to
find simple reproducer for the same.

Pl. find the reproducer for the same with this issue is hitting easily.  

Logs : 

./sim ext4_write
creating the threads
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader thread has opened the file, fd : 4
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
reader..checking data integrity
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
writing B at offset 0...
writing A at offset 0...
writing B at offset 0...
reader..checking data integrity
writing A at offset 0...
reader.. corrupted data, at offset : 511
writing B at offset 0...



C program :
#include <stdio.h>
#include <fcntl.h>
#include <pthread.h>
#include <assert.h>
#include <errno.h>
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>
       #include <unistd.h>
#include <sys/mman.h>

pthread_t reader_id, writer_id;

char write_buf [4096] = {0,};
char read_buf[4096] = {0,};

char  datafile[256] = {0,};
int stop_write = 0;



void * writer (void * arg)
{

        int fd = -1;
        int count = 0;
        /* this thread will open the file and write 4k data to it alternatively
         * of a different data set to the same offset
         */
        /* opening the file */
        assert((fd = open(datafile, O_CREAT|O_RDWR, 0777)) != -1);

        while (1) {

                if (stop_write)
                {
                        close(fd);
                        printf("write stopped\n");
                        return NULL;
                }
                if (count % 2 == 0)
                        memset(write_buf, 'A', sizeof(write_buf));
                else
                        memset(write_buf, 'B', sizeof(write_buf));


                assert(lseek(fd, 0, SEEK_SET) == 0);
                printf("writing %c at offset 0...\n", write_buf[0]);
                assert(write(fd, write_buf, 4096) == 4096);
                count ++;

        }
        //pthread_exit((void *)0);
        close(fd);
        return NULL;
}

void * reader(void * arg)
{

        int fd = -1;
        int count = 0;
        /* this thread will open the file and write 4k data to it alternatively
         * of a different data set to the same offset
         */
        /* opening the file */
        assert((fd = open(datafile, O_CREAT|O_RDWR, 0777)) != -1);
        printf("reader thread has opened the file, fd : %d\n", fd);
        while (1) {

                memset(read_buf, '\0', 4096);
                assert(lseek(fd, 0, SEEK_SET) == 0);
                assert(read(fd, read_buf, 4096) == 4096);
                count ++;
                printf("reader..checking data integrity\n");
                int i=0;
                for (i=0; i < 4095; i++)
                {
                        int prev_char = read_buf[i];
                        int next_char = read_buf[i+1];
                        if (prev_char != next_char)
                        {
                                printf("reader.. corrupted data, at offset :
%d\n", i);
                                stop_write = 1;
                                int output_fd = open("res.txt", O_CREAT|O_RDWR,
0777);

                                assert(write(output_fd, read_buf, 4096) ==
4096);
                                close(output_fd);
                                close(fd);
                                return NULL;
                        }
                }


        }
        //pthread_exit((void *)0);
        close(fd);
        return NULL;
}
int main (int argc, char *argv[])
{
        pthread_attr_t attr;
        void * arg = NULL;
        int *status;
        int err = 0;

        if (argc != 2) {
                printf("usage : ./reader_writer <file pathname>\n");
                exit(1);
        }


        memset(datafile, '\0', sizeof(datafile));
        strcpy(datafile, argv[1]);

        pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

        /* create the reader and writer thread */
        printf("creating the threads\n");
        if ((err = pthread_create(&writer_id, &attr, writer, (void *)arg)) !=
0) {
                printf ("pthread_create failed err no :%d\n", err);
        }
        if ((err = pthread_create(&reader_id, &attr, reader, (void *)arg)) !=
0) {
                printf ("pthread_create failed err no :%d\n", err);
        }
        pthread_attr_destroy(&attr);

        /* Wait on the other threads */
        assert(pthread_join(writer_id, (void *)&status) == 0);
        assert(pthread_join(reader_id, (void *)&status) == 0);

        pthread_exit(NULL);
}

How to run
gcc program.c -o ext4_program -lpthread 
./ext4_program ext4_write

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