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05 April 2024, 19:05:47 UTC
Revision 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC, committed by Chris Mason on 25 November 2015, 13:22:08 UTC 
Btrfs: fix scrub preventing unused block groups from being deleted
 
Currently scrub can race with the cleaner kthread when the later attempts
to delete an unused block group, and the result is preventing the cleaner
kthread from ever deleting later the block group - unless the block group
becomes used and unused again. The following diagram illustrates that
race:

              CPU 1                                 CPU 2

 cleaner kthread
   btrfs_delete_unused_bgs()

     gets block group X from
     fs_info->unused_bgs and
     removes it from that list

                                             scrub_enumerate_chunks()

                                               searches device tree using
                                               its commit root

                                               finds device extent for
                                               block group X

                                               gets block group X from the tree
                                               fs_info->block_group_cache_tree
                                               (via btrfs_lookup_block_group())

                                               sets bg X to RO

     sees the block group is
     already RO and therefore
     doesn't delete it nor adds
     it back to unused list

So fix this by making scrub add the block group again to the list of
unused block groups if the block group is still unused when it finished
scrubbing it and it hasn't been removed already.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
1 parent 020d5b7
Raw File
Tip revision: 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC
Btrfs: fix scrub preventing unused block groups from being deleted
Tip revision: 758f2df
Kconfig.debug 
config PAGE_EXTENSION
	bool "Extend memmap on extra space for more information on page"
	---help---
	  Extend memmap on extra space for more information on page. This
	  could be used for debugging features that need to insert extra
	  field for every page. This extension enables us to save memory
	  by not allocating this extra memory according to boottime
	  configuration.

config DEBUG_PAGEALLOC
	bool "Debug page memory allocations"
	depends on DEBUG_KERNEL
	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
	depends on !KMEMCHECK
	select PAGE_EXTENSION
	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
	---help---
	  Unmap pages from the kernel linear mapping after free_pages().
	  This results in a large slowdown, but helps to find certain types
	  of memory corruption.

	  For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
	  fill the pages with poison patterns after free_pages() and verify
	  the patterns before alloc_pages().  Additionally,
	  this option cannot be enabled in combination with hibernation as
	  that would result in incorrect warnings of memory corruption after
	  a resume because free pages are not saved to the suspend image.

config PAGE_POISONING
	bool
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