Re: 2.6.20-rc6-mm1

Anton Altaparmakov
2007-01-30T20:50:21Z

Hi Andrew,

Looks good for NTFS thanks! The only thing is that I think we
already have a variable "unsigned long flags" in the function
ntfs_end_buffer_async_read() so that could be used instead of
redefining it more locally in the if statements.

Could you send the patch to Linus?

Feel free to add my Acked-by or Signed-off-by "Anton Altaparmakov
<aia21@cantab.net> line if you wish (I am not bothered either way)...

Thanks a lot for fixing it!

Best regards,

Anton

On Tue, 30 Jan 2007, Andrew Morton wrote:

> 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);
> _
>
>

Best regards,

Anton
--
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/