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SubjectRe: [PATCH linux-2.6.0-test10-mm1] dio-read-race-fix
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I've done more testing with added debug code.

It looks like the filemap_write_and_wait() call is returning
with data that has not made it disk.

I added code to filemap_write_and_wait() to check if
mapping->dirty_pages is not empty after calling filemap_fdatawrite()
and filemap_fdatawait() and retry. Even with the retry, the test still
sees uninitialized data when running tests overnight (I added a printk
so I know the retry is happening). There are pages left on the
dirty_pages list even after the write and wait.

I've added a bunch more debug code and am currently running the test
again to see if I can find out what is going on.

I'll send more email when I know more.

Daniel



On Mon, 2003-12-08 at 10:23, Daniel McNeil wrote:
> 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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