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Revision ad576e63e0c8b274a8558b8e05a6d0526e804dc0 authored by Nick Piggin on 05 May 2005, 23:15:46 UTC, committed by Linus Torvalds on 05 May 2005, 23:36:40 UTC 
[PATCH] __block_write_full_page race fix
 
When running
	fsstress -v -d $DIR/tmp -n 1000 -p 1000 -l 2
on an ext2 filesystem with 1024 byte block size, on SMP i386 with 4096 byte
page size over loopback to an image file on a tmpfs filesystem, I would
very quickly hit
	BUG_ON(!buffer_async_write(bh));
in fs/buffer.c:end_buffer_async_write

It seems that more than one request would be submitted for a given bh
at a time.

What would happen is the following:
2 threads doing __mpage_writepages on the same page.
Thread 1 - lock the page first, and enter __block_write_full_page.
Thread 1 - (eg.) mark_buffer_async_write on the first 2 buffers.
Thread 1 - set page writeback, unlock page.
Thread 2 - lock page, wait on page writeback
Thread 1 - submit_bh on the first 2 buffers.
=> both requests complete, none of the page buffers are async_write,
   end_page_writeback is called.
Thread 2 - wakes up. enters __block_write_full_page.
Thread 2 - mark_buffer_async_write on (eg.) the last buffer
Thread 1 - finds the last buffer has async_write set, submit_bh on that.
Thread 2 - submit_bh on the last buffer.
=> oops.

So change __block_write_full_page to explicitly keep track of the last bh
we need to issue, so we don't touch anything after issuing the last
request.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent f3ddbdc
Raw File
Makefile 

obj-y := initramfs_data.o

hostprogs-y  := gen_init_cpio

clean-files := initramfs_data.cpio.gz initramfs_list

# initramfs_data.o contains the initramfs_data.cpio.gz image.
# The image is included using .incbin, a dependency which is not
# tracked automatically.
$(obj)/initramfs_data.o: $(obj)/initramfs_data.cpio.gz FORCE

ifdef CONFIG_INITRAMFS_ROOT_UID
gen_initramfs_args += -u $(CONFIG_INITRAMFS_ROOT_UID)
endif

ifdef CONFIG_INITRAMFS_ROOT_GID
gen_initramfs_args += -g $(CONFIG_INITRAMFS_ROOT_GID)
endif

# The $(shell echo $(CONFIG_INITRAMFS_SOURCE)) is to remove the
# gratuitous begin and end quotes from the Kconfig string type.
# Internal, escaped quotes in the Kconfig string will loose the
# escape and become active quotes.
quotefixed_initramfs_source := $(shell echo $(CONFIG_INITRAMFS_SOURCE))

filechk_initramfs_list = $(CONFIG_SHELL) \
 $(srctree)/scripts/gen_initramfs_list.sh $(gen_initramfs_args) $(quotefixed_initramfs_source)

$(obj)/initramfs_list: FORCE
	$(call filechk,initramfs_list)

quiet_cmd_cpio = CPIO    $@
      cmd_cpio = ./$< $(obj)/initramfs_list > $@


# Check if the INITRAMFS_SOURCE is a cpio archive
ifneq (,$(findstring .cpio,$(quotefixed_initramfs_source)))

# INITRAMFS_SOURCE has a cpio archive - verify that it's a single file
ifneq (1,$(words $(quotefixed_initramfs_source)))
$(error Only a single file may be specified in CONFIG_INITRAMFS_SOURCE (="$(quotefixed_initramfs_source)") when a cpio archive is directly specified.)
endif
# Now use the cpio archive directly
initramfs_data_cpio = $(quotefixed_initramfs_source)
targets += $(quotefixed_initramfs_source)

else

# INITRAMFS_SOURCE is not a cpio archive - create one
$(obj)/initramfs_data.cpio: $(obj)/gen_init_cpio \
                            $(initramfs-y) $(obj)/initramfs_list FORCE
	$(call if_changed,cpio)

targets += initramfs_data.cpio
initramfs_data_cpio = $(obj)/initramfs_data.cpio

endif


$(obj)/initramfs_data.cpio.gz: $(initramfs_data_cpio) FORCE
	$(call if_changed,gzip)

targets += initramfs_data.cpio.gz
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