Re: 2.6.20-rc6-mm1

Andrew Morton
2007-01-30T19:32:06Z

On Mon, 29 Jan 2007 23:27:27 -0800
Andrew Morton <akpm@osdl.org> wrote:

> On Sun, 28 Jan 2007 11:25:42 +0100
> Jiri Slaby <jirislaby@gmail.com> wrote:
>
> > Andrew Morton napsal(a):
> > > Temporarily at
> > >
> > > http://userweb.kernel.org/~akpm/2.6.20-rc6-mm1/
> >
> > I'm still seeing this during bootup:
> > BUG: at /home/l/latest/xxx/arch/i386/mm/highmem.c:52 kmap_atomic()
> > [<c0104ffb>] show_trace_log_lvl+0x1a/0x30
> > [<c01056b5>] show_trace+0x12/0x14
> > [<c010573c>] dump_stack+0x16/0x18
> > [<c011b24f>] kmap_atomic+0x16c/0x20e
> > [<c01b279e>] ntfs_end_buffer_async_read+0x18e/0x2ed
> > [<c0183352>] end_bio_bh_io_sync+0x26/0x3f
> > [<c0184dd4>] bio_endio+0x37/0x62
> > [<c01cda43>] __end_that_request_first+0x224/0x444
> > [<c01cdc6b>] end_that_request_chunk+0x8/0xa
> > [<c024507d>] scsi_end_request+0x1f/0xc7
> > [<c02451e6>] scsi_io_completion+0x7b/0x33a
> > [<c024aa5d>] sd_rw_intr+0x23/0x1ab
> > [<c02415ed>] scsi_finish_command+0x42/0x47
> > [<c0245a38>] scsi_softirq_done+0x64/0xcf
> > [<c01cf9e6>] blk_done_softirq+0x54/0x62
> > [<c0127bc5>] __do_softirq+0x75/0xde
> > [<c0127c69>] do_softirq+0x3b/0x3d
> > [<c0127ee6>] irq_exit+0x3b/0x3d
> > [<c0106804>] do_IRQ+0x51/0x8d
> > [<c0104a5f>] common_interrupt+0x23/0x28
> > [<c010241a>] cpu_idle+0x80/0xc3
> > [<c010140d>] rest_init+0x23/0x36
> > [<c045ea59>] start_kernel+0x3a5/0x43c
> > [<00000000>] 0x0
> > =======================
> >
> > I.e. KM_BIO_SRC_IRQ through softirq path.
> >
>
> argh.
>
> ntfs_end_buffer_async_read() doesn't know whether it will be called from
> hardirq or from softirq context: it depends upon the underlying driver.
>
> In this case, if the CPU running ntfs_end_buffer_async_read() is
> interrupted by IO completion against a different disk controller and that
> completion handler uses KM_BIO_SRC_IRQ (as it is allowed to do), it will
> trash ntfs_end_buffer_async_read()'s atomic kmap and unpleasing things will
> ensue.
>
> I guess a suitable fix here is to protect that kmap with
> local_irq_save/restore.
>
> I wonder where else we have that bug?

Actually, this isn't related to softirq-vs-hardirq. Most interrupt
handlers are interruptible, so the rule is simply that KM_BIO_SRC_IRQ must
always be taken under local_irq_disable().

A quick scan indicates that the following files might be buggy in this
regard:

drivers/mmc/wbsd.c
drivers/mmc/at91_mci.c
drivers/mmc/sdhci.c
drivers/scsi/scsi_lib.c when called from stex.c
fs/ntfs/aops.c

Happily, KM_BIO_DST_IRQ has no users and can presumably be removed.

Fixes for stex and ntfs follow.

From: Andrew Morton <akpm@osdl.org>

The KM_BIO_SRC_IRQ kmap slot requires local irq protection.

Cc: James Bottomley <James.Bottomley@steeleye.com>
Cc: Ed Lin <ed.lin@promise.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

drivers/scsi/stex.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff -puN drivers/scsi/stex.c~stex-kmap_atomic-atomicity-fix drivers/scsi/stex.c
--- a/drivers/scsi/stex.c~stex-kmap_atomic-atomicity-fix
+++ a/drivers/scsi/stex.c
@@ -459,15 +459,19 @@ static void stex_internal_copy(struct sc
*count = cmd->request_bufflen;
lcount = *count;
while (lcount) {
+ unsigned long flags = flags; /* Suppress uninit warning */
+
len = lcount;
s = (void *)src;
if (cmd->use_sg) {
size_t offset = *count - lcount;
s += offset;
+ local_irq_save(flags);
base = scsi_kmap_atomic_sg(cmd->request_buffer,
sg_count, &offset, &len);
if (base == NULL) {
*count -= lcount;
+ local_irq_restore(flags);
return;
}
d = base + offset;
@@ -480,8 +484,10 @@ static void stex_internal_copy(struct sc
memcpy(s, d, len);

lcount -= len;
- if (cmd->use_sg)
+ if (cmd->use_sg) {
scsi_kunmap_atomic_sg(base);
+ local_irq_restore(flags);
+ }
}
}

_

From: Andrew Morton <akpm@osdl.org>

The KM_BIO_SRC_IRQ kmap slot requires local irq protection.

Cc: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

fs/ntfs/aops.c | 6 ++++++
1 file changed, 6 insertions(+)

diff -puN fs/ntfs/aops.c~ntfs-kmap_atomic-atomicity-fix fs/ntfs/aops.c
--- a/fs/ntfs/aops.c~ntfs-kmap_atomic-atomicity-fix
+++ a/fs/ntfs/aops.c
@@ -88,14 +88,17 @@ static void ntfs_end_buffer_async_read(s
if (unlikely(file_ofs + bh->b_size > init_size)) {
u8 *kaddr;
int ofs;
+ unsigned long flags;

ofs = 0;
if (file_ofs < init_size)
ofs = init_size - file_ofs;
+ local_irq_save(flags);
kaddr = kmap_atomic(page, KM_BIO_SRC_IRQ);
memset(kaddr + bh_offset(bh) + ofs, 0,
bh->b_size - ofs);
kunmap_atomic(kaddr, KM_BIO_SRC_IRQ);
+ local_irq_restore(flags);
flush_dcache_page(page);
}
} else {
@@ -138,16 +141,19 @@ static void ntfs_end_buffer_async_read(s
u8 *kaddr;
unsigned int i, recs;
u32 rec_size;
+ unsigned long flags;

rec_size = ni->itype.index.block_size;
recs = PAGE_CACHE_SIZE / rec_size;
/* Should have been verified before we got here... */
BUG_ON(!recs);
+ local_irq_save(flags);
kaddr = kmap_atomic(page, KM_BIO_SRC_IRQ);
for (i = 0; i < recs; i++)
post_read_mst_fixup((NTFS_RECORD*)(kaddr +
i * rec_size), rec_size);
kunmap_atomic(kaddr, KM_BIO_SRC_IRQ);
+ local_irq_restore(flags);
flush_dcache_page(page);
if (likely(page_uptodate && !PageError(page)))
SetPageUptodate(page);
_