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    SubjectRe: [PATCH linux-2.6.0-test10-mm1] dio-read-race-fix
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    My patch did not fix the problem. :(

    The tests over the weekend reported bad data.

    The sampling of the i_size after dropping i_sem still looks wrong
    to me. I will keep looking and see if I can find another problem.


    Daniel

    On Fri, 2003-12-05 at 17:29, Daniel McNeil wrote:
    > Janet,
    >
    > I think I found the problem that is causing the dio reads to get
    > unintialized data with buffer writes. i_size is sampled after
    > i_sem is dropped and after the i/o have completed. i_size could
    > have changed in the mean time. This patch samples i_size before
    > dropping i_sem. I'll leave the test running over the weekend to
    > verify.
    >
    > Daniel
    >
    > On Tue, 2003-12-02 at 18:33, Janet Morgan wrote:
    > > Hi Suparna, Daniel,
    > >
    > > Just wanted to let you know that I seem to be hitting a failure when I
    > > run the testcase (attached) that Stephen Tweedie wrote to expose the DIO
    > > races (the testcase issues buffered writes and dio reads). I'm trying to
    > > debug the failure, but I know it will be slow going for me.
    > >
    > > I hit the problem when I run multiple instances of the test against
    > > the same filesystem (I do specify a unique file for each instance of
    > > the test). I normally run about 6 instances of the test, e.g.,
    > > "direct_read_under foo1", "direct_read_under foo2", etc. The test
    > > runs in an infinite loop until a data mis-compare is detected.
    > > I have not been able to reproduce the failure when I restrict each
    > > instance of the test to its own filesystem.
    > >
    > > I've tried running with the combinations below and I eventually
    > > get a failure in each case. I assume all but the last combo includes
    > > the critical aio/dio fixes for the associated base.
    > >
    > > Combinations tested:
    > >
    > > Daniel's latest:
    > > 2.6.0-test9-mm5 +
    > > aio-dio-fallback-bio_count-race.patch +
    > > direct-io-memleak-fix.patch
    > >
    > > Suparna's latest:
    > > 2.6.0-test9-mm5 +
    > > Suparna's current patches:
    > >
    > > http://marc.theaimsgroup.com/?l=linux-aio&m=106983304420570&w=2 +
    > >
    > > http://marc.theaimsgroup.com/?l=linux-kernel&m=106904658121299&w=2 +
    > > direct-io-memleak-fix.patch
    > >
    > > stock linux-2.6.0-test9 plus:
    > > aio-refcnt.patch +
    > > dio-aio-fixes.patch +
    > > dio-aio-fixes-fixes.patch +
    > > O_DIRECT-race-fixes-rollup.patch
    > >
    > > stock linux-2.6.0-test11 plus:
    > > O_DIRECT-race-fixes-rollup.patch
    > >
    > > Thanks,
    > > -Janet
    > >
    > > ______________________________________________________________________
    > >
    > > #define _XOPEN_SOURCE 600
    > > #define _GNU_SOURCE
    > >
    > > #include <unistd.h>
    > > #include <stdlib.h>
    > > #include <stdio.h>
    > > #include <string.h>
    > > #include <errno.h>
    > > #include <sys/fcntl.h>
    > > #include <sys/mman.h>
    > > #include <sys/wait.h>
    > >
    > > #define BIGSIZE 128*1024*1024
    > > #define READSIZE 32*1024*1024
    > > #define WRITESIZE 32*1024*1024
    > >
    > > int pagesize;
    > > char *iobuf;
    > >
    > > void assert(const char *what, int assertion)
    > > {
    > > if (assertion)
    > > return;
    > > perror(what);
    > > exit(1);
    > > }
    > >
    > > void do_buffered_writes(int fd, int pattern)
    > > {
    > > int rc;
    > > int offset;
    > >
    > > memset(iobuf, pattern, WRITESIZE);
    > > for (offset = 0; offset+WRITESIZE <= BIGSIZE; offset += WRITESIZE) {
    > > rc = pwrite(fd, iobuf, WRITESIZE, offset);
    > > assert("pwrite", rc >= 0);
    > > if (rc != WRITESIZE) {
    > > fprintf(stderr, "short write (%d out of %d)\n",
    > > rc, WRITESIZE);
    > > exit(1);
    > > }
    > > fsync(fd);
    > > }
    > > }
    > >
    > > int do_direct_reads(char *filename)
    > > {
    > > int fd;
    > > int offset;
    > > int rc, i;
    > > int *p;
    > >
    > > fd = open(filename, O_DIRECT|O_RDONLY, 0);
    > > assert("open", fd >= 0);
    > >
    > > for (offset = 0; offset+READSIZE <= BIGSIZE; offset += READSIZE) {
    > > rc = pread(fd, iobuf, READSIZE, offset);
    > > assert("pread", rc >= 0);
    > > if (rc != READSIZE) {
    > > fprintf(stderr, "short read (%d out of %d)\n",
    > > rc, READSIZE);
    > > exit(1);
    > > }
    > > for (i=0, p=(int *)iobuf; i<READSIZE; i+=4) {
    > > if (*p) {
    > > fprintf(stderr,
    > > "Found data (%08x) at offset %d+%d\n",
    > > *p, offset, i);
    > > return 1;
    > > }
    > > p++;
    > > }
    > > }
    > > return 0;
    > > }
    > >
    > > int main(int argc, char *argv[])
    > > {
    > > char *filename;
    > > int fd;
    > > int pid;
    > > int err;
    > > int pass = 0;
    > > int bufsize;
    > >
    > > if (argc != 2) {
    > > fprintf(stderr, "Needs a filename as an argument.\n");
    > > exit(1);
    > > }
    > >
    > > filename = argv[1];
    > >
    > > pagesize = getpagesize();
    > > bufsize = READSIZE;
    > > if (WRITESIZE > READSIZE)
    > > bufsize = WRITESIZE;
    > > err = posix_memalign((void**) &iobuf, pagesize, bufsize);
    > > if (err) {
    > > fprintf(stderr, "Error allocating %d aligned bytes.\n", bufsize);
    > > exit(1);
    > > }
    > >
    > > fd = open(filename, O_CREAT|O_TRUNC|O_RDWR, 0666);
    > > assert("open", fd >= 0);
    > >
    > > do {
    > > printf("Pass %d...\n", ++pass);
    > >
    > > assert("ftruncate", ftruncate(fd, BIGSIZE) == 0);
    > > fsync(fd);
    > >
    > > pid = fork();
    > > assert("fork", pid >= 0);
    > >
    > > if (!pid) {
    > > do_buffered_writes(fd, 0);
    > > exit(0);
    > > }
    > >
    > > err = do_direct_reads(filename);
    > >
    > > wait4(pid, NULL, WNOHANG, 0);
    > >
    > > if (err)
    > > break;
    > >
    > > /* Fill the file with a known pattern so that the blocks
    > > * on disk can be detected if they become exposed. */
    > > do_buffered_writes(fd, 1);
    > > fsync(fd);
    > >
    > > assert("ftruncate", ftruncate(fd, 0) == 0);
    > > fsync(fd);
    > > } while (1);
    > >
    > > return err;
    > > }
    > >

    -
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