On Wed, 28 Jun 2006 15:19:55 +0200
Paolo Ornati <[email protected]> wrote:
> > > > [ 430.083347] localedef R running task 0 8577 8558 8578 (NOTLB)
> > > > [ 430.083352] gzip X ffff81001e612ee0 0 8578 8577 (L-TLB)
> > > > [ 430.083358] ffff81001395bef8 ffff81001fd1a310 0000000000000246 ffff81001e612ee0
> > > > [ 430.083362] ffff81001e4c0080 ffff81001e612ee0 ffff81001e4c0258 0000000000000001
> > > > [ 430.083366] 0000000000000046 0000000000000046 ffff81001395bf18 0000000000000010
> > > > [ 430.083370] Call Trace: <ffffffff80227f6f>{do_exit+2378} <ffffffff802628e9>{vfs_write+288}
> > > > [ 430.083379] <ffffffff80228065>{sys_exit_group+0} <ffffffff80209806>{system_call+126}
> > >
> > > do_exit() -- kernel/exit.c
> > >
> > > 0xffffffff80227f66 <do_exit+2369>: mov %rax,0x18(%rbp)
> > > 0xffffffff80227f6a <do_exit+2373>: callq 0xffffffff8048b850 <schedule>
> > > 0xffffffff80227f6f <do_exit+2378>: ud2a
> > > 0xffffffff80227f71 <do_exit+2380>: pushq $0xffffffff804b7821
> > > 0xffffffff80227f76 <do_exit+2385>: retq $0x3ba
> > > 0xffffffff80227f79 <do_exit+2388>: jmp 0xffffffff80227f79 <do_exit+2388>
> >
> >
> > that is the end of the function:
> >
> > ...
> > schedule();
> > BUG();
> > /* Avoid "noreturn function does return". */
> > for (;;) ;
> > }
> >
> >
> > So the questions are two:
> >
> > 1) why schedule() didn't work?
> >
> > 2) why the process is looping around "ud2a" (placed by BUG()) and
> > presumibly throwing a lot of "invalid opcode" exceptions?
>
> It seems that the first mail didn't hit LKML (maybe it was too big),
> here it is (stripped):
>
> ------------------------------------------------------------------------
> Running "localedef" triggers an infinite loop in kernel mode (or
> something) --> localdef becomes unkillable.
>
> This is dmesg after pressing ALT+SysRQ+T three times:
>
> [CUT]
>
> KERNEL:
>
> --
> Paolo Ornati
> Linux 2.6.17-ga39727f2-dirty on x86_64
> ^^^^^^^
>
> The -dirty is because of a fix to PS2 Keyboard auto-repeat, nothing else.
> ------------------------------------------------------------------------
Hi everybody,
as you can see from the subject the problem is an unkillable process
(localedef) that eats 100% CPU (the system is usable however).
After a git-bisect session I've found that reverting the following
commit fixes the problem.
Any idea?
commit 6527c2bdf1f833cc18e8f42bd97973d583e4aa83
Author: Vladimir V. Saveliev <[email protected]>
Date: Tue Jun 27 02:53:57 2006 -0700
[PATCH] generic_file_buffered_write(): deadlock on vectored write
generic_file_buffered_write() prefaults in user pages in order to avoid
deadlock on copying from the same page as write goes to.
However, it looks like there is a problem when write is vectored:
fault_in_pages_readable brings in current segment or its part (maxlen).
OTOH, filemap_copy_from_user_iovec is called to copy number of bytes
(bytes) which may exceed current segment, so filemap_copy_from_user_iovec
switches to the next segment which is not brought in yet. Pagefault is
generated. That causes the deadlock if pagefault is for the same page
write goes to: page being written is locked and not uptodate, pagefault
will deadlock trying to lock locked page.
[[email protected]: somewhat rewritten]
Cc: Neil Brown <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/mm/filemap.c b/mm/filemap.c
index 9c7334b..d504d6e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2095,14 +2095,21 @@ generic_file_buffered_write(struct kiocb
do {
unsigned long index;
unsigned long offset;
- unsigned long maxlen;
size_t copied;
offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
index = pos >> PAGE_CACHE_SHIFT;
bytes = PAGE_CACHE_SIZE - offset;
- if (bytes > count)
- bytes = count;
+
+ /* Limit the size of the copy to the caller's write size */
+ bytes = min(bytes, count);
+
+ /*
+ * Limit the size of the copy to that of the current segment,
+ * because fault_in_pages_readable() doesn't know how to walk
+ * segments.
+ */
+ bytes = min(bytes, cur_iov->iov_len - iov_base);
/*
* Bring in the user page that we will copy from _first_.
@@ -2110,10 +2117,7 @@ generic_file_buffered_write(struct kiocb
* same page as we're writing to, without it being marked
* up-to-date.
*/
- maxlen = cur_iov->iov_len - iov_base;
- if (maxlen > bytes)
- maxlen = bytes;
- fault_in_pages_readable(buf, maxlen);
+ fault_in_pages_readable(buf, bytes);
page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
if (!page) {
--
Paolo Ornati
Linux 2.6.17.1 on x86_64
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