When testing AIO on PPC64 (a power5 machine) running 2.6.11 with
CONFIG_HUGETLB_PAGE=y, I ran into a kernel panic when a process exits that has
done AIO (io_queue_init()) but has not done the io_queue_release(). The
exit_aio() code is cleaning up and panicing when trying to free the aio ring
buffer.
I tracked this down to is_hugepage_only_range() (include/asm-ppc64/page.h)
which is doing a touches_hugepage_low_range() which is checking
current->mm->context.htlb_segs. The problem is that exit_mm()
cleared tsk->mm before doing the mmput() which leads to the exit_aio()
and then the panic. Looks like is_hugepage_only_range() is only used
in ia64 and ppc64. Possible fix is to change is_hugepage_only_range()
to take an 'mm' as a parameter as well as 'addr' and 'len' and then
the ppc64 code could change to use 'mm'. It looks like it has been
broken for quite a while.
Here's the stack trace:
cpu 0x2: Vector: 300 (Data Access) at [c0000001d1be7590]
pc: c000000000092960: .unmap_region+0x17c/0x4a4
lr: c000000000092bb0: .unmap_region+0x3cc/0x4a4
sp: c0000001d1be7810
msr: 8000000000009032
dar: 298
dsisr: 40000000
current = 0xc000000001dd77b0
paca = 0xc000000000595c00
pid = 11336, comm = aiodio_readoff
[c0000001d1be78e0] c000000000093d08 .do_munmap+0x240/0x408
[c0000001d1be79b0] c0000000000d11b4 .aio_free_ring+0x10c/0x1d8
[c0000001d1be7a50] c0000000000d162c .__put_ioctx+0x84/0x120
[c0000001d1be7af0] c0000000000d3640 .exit_aio+0xf4/0x100
[c0000001d1be7b80] c00000000004dfd4 .mmput+0x80/0x15c
[c0000001d1be7c20] c000000000053648 .exit_mm+0x1b4/0x264
[c0000001d1be7cc0] c0000000000555ac .do_exit+0x10c/0xdb0
[c0000001d1be7d90] c0000000000562a8 .do_group_exit+0x58/0xd8
[c0000001d1be7e30] c00000000000d500 syscall_exit+0x0/0x18
Here's a program that produces the panic:
(compile using cc -o aiodio_read aiodio_read.c -laio).
--------------------------
#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>
#include <sys/stat.h>
#include <libaio.h>
int pagesize;
char *iobuf;
io_context_t myctx;
int aio_maxio = 4;
/*
* do a AIO DIO write
*/
int do_aio_direct_read(int fd, char *iobuf, int offset, int size)
{
struct iocb myiocb;
struct iocb *iocbp = &myiocb;
int ret;
struct io_event e;
struct stat s;
io_prep_pread(&myiocb, fd, iobuf, size, offset);
if ((ret = io_submit(myctx, 1, &iocbp)) != 1) {
perror("io_submit");
return ret;
}
ret = io_getevents(myctx, 1, 1, &e, 0);
if (ret) {
struct iocb *iocb = e.obj;
int iosize = iocb->u.c.nbytes;
char *buf = iocb->u.c.buf;
long long loffset = iocb->u.c.offset;
printf("AIO read of %d at offset %lld returned %d\n",
iosize, loffset, e.res);
}
return ret;
}
int main(int argc, char *argv[])
{
char *filename;
int fd;
int err;
filename = "test.aio.file";
fd = open(filename, O_RDWR|O_DIRECT|O_CREAT|O_TRUNC, 0666);
pagesize = getpagesize();
err = posix_memalign((void**) &iobuf, pagesize, pagesize);
if (err) {
fprintf(stderr, "Error allocating %d aligned bytes.\n",
pagesize);
exit(1);
}
err = write(fd, iobuf, pagesize);
if (err != pagesize) {
fprintf(stderr, "Error ret = %d writing %d bytes.\n",
err, pagesize);
perror("");
exit(1);
}
memset(&myctx, 0, sizeof(myctx));
io_queue_init(aio_maxio, &myctx);
err = do_aio_direct_read(fd, iobuf, 0, pagesize);
close(fd);
printf("This will panic on ppc64\n");
return err;
}
--------------------------
Daniel
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