* Possible deadlock with ->writepaged version of flush_dirty_buffers() and 2.4.0
@ 2001-01-10 19:56 Marcelo Tosatti
2001-01-11 15:43 ` Chris Mason
0 siblings, 1 reply; 2+ messages in thread
From: Marcelo Tosatti @ 2001-01-10 19:56 UTC (permalink / raw)
To: Chris Mason; +Cc: linux-kernel
Hi Chris,
It seems there is a possible deadlock condition with your patch which
changes flush_dirty_buffers() to use ->writepage (something which we
_definately_ want for 2.5). Take a look:
mark_buffer_dirty->balance_dirty->wakeup_bdflush->flush_dirty_buffers->
writepage->block_write_full_page->__block_write_full_page->get_block->
ext2_get_block->ext2_alloc_branch->
ext2_alloc_block->ext2_new_block->lock_super
or
getblk()->lock_super
I dont see any reason why this deadlock could'nt happen in practice now.
If I'm right, it will pretty nasty to fix this. One possible solution is
to _never_ call mark_buffer_dirty() with the superblock lock held (ext2
has a lot of places likes this right now)
Comments?
-
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* Re: Possible deadlock with ->writepaged version of flush_dirty_buffers() and 2.4.0
2001-01-10 19:56 Possible deadlock with ->writepaged version of flush_dirty_buffers() and 2.4.0 Marcelo Tosatti
@ 2001-01-11 15:43 ` Chris Mason
0 siblings, 0 replies; 2+ messages in thread
From: Chris Mason @ 2001-01-11 15:43 UTC (permalink / raw)
To: Marcelo Tosatti; +Cc: linux-kernel
On Wednesday, January 10, 2001 05:56:09 PM -0200 Marcelo Tosatti
<marcelo@conectiva.com.br> wrote:
>
> Hi Chris,
>
> It seems there is a possible deadlock condition with your patch which
> changes flush_dirty_buffers() to use ->writepage (something which we
> _definately_ want for 2.5). Take a look:
>
Yes, good catch.
>
> mark_buffer_dirty->balance_dirty->wakeup_bdflush->flush_dirty_buffers->
> writepage->block_write_full_page->__block_write_full_page->get_block->
> ext2_get_block->ext2_alloc_branch->
>
> ext2_alloc_block->ext2_new_block->lock_super
> or
> getblk()->lock_super
>
>
> I dont see any reason why this deadlock could'nt happen in practice now.
>
It won't happen until someone other than fs/buffer.c starts marking ext2
pages dirty. The normal file write path will make sure that any dirty
buffers are mapped, so the ext2_get_block code is never run.
> If I'm right, it will pretty nasty to fix this. One possible solution is
> to _never_ call mark_buffer_dirty() with the superblock lock held (ext2
> has a lot of places likes this right now)
>
This is probably the best solution, since it is a good idea regardless of
my patch.
-chris
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