Skip to main content

Browse the archive

https://github.com/torvalds/linux
17 May 2024, 11:00:25 UTC
Revision 5b808a2300a5ac45f4798ebfac8b367e98a4b692 authored by Krzysztof Kozlowski on 16 October 2013, 20:47:06 UTC, committed by Linus Torvalds on 17 October 2013, 04:35:53 UTC 
swap: fix set_blocksize race during swapon/swapoff
 
Fix race between swapoff and swapon.  Swapoff used old_block_size from
swap_info outside of swapon_mutex so it could be overwritten by
concurrent swapon.

The race has visible effect only if more than one swap block device
exists with different block sizes (e.g.  /dev/sda1 with block size 4096
and /dev/sdb1 with 512).  In such case it leads to setting the blocksize
of swapped off device with wrong blocksize.

The bug can be triggered with multiple concurrent swapoff and swapon:
0. Swap for some device is on.
1. swapoff:
First the swapoff is called on this device and "struct swap_info_struct
*p" is assigned. This is done under swap_lock however this lock is
released for the call try_to_unuse().

2. swapon:
After the assignment above (and before acquiring swapon_mutex &
swap_lock by swapoff) the swapon is called on the same device.
The p->old_block_size is assigned to the value of block_size the device.
This block size should be the same as previous but sometimes it is not.
The swapon ends successfully.

3. swapoff:
Swapoff resumes, grabs the locks and mutex and continues to disable this
swap device. Now it sets the block size to value taken from swap_info
which was overwritten by swapon in 2.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reported-by: Weijie Yang <weijie.yang.kh@gmail.com>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Shaohua Li <shli@fusionio.com>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent fad1a86
Raw File
Tip revision: 5b808a2300a5ac45f4798ebfac8b367e98a4b692 authored by Krzysztof Kozlowski on 16 October 2013, 20:47:06 UTC
swap: fix set_blocksize race during swapon/swapoff
Tip revision: 5b808a2
Kbuild 
#
# Kbuild for top-level directory of the kernel
# This file takes care of the following:
# 1) Generate bounds.h
# 2) Generate asm-offsets.h (may need bounds.h)
# 3) Check for missing system calls

#####
# 1) Generate bounds.h

bounds-file := include/generated/bounds.h

always  := $(bounds-file)
targets := $(bounds-file) kernel/bounds.s

quiet_cmd_bounds = GEN     $@
define cmd_bounds
	(set -e; \
	 echo "#ifndef __LINUX_BOUNDS_H__"; \
	 echo "#define __LINUX_BOUNDS_H__"; \
	 echo "/*"; \
	 echo " * DO NOT MODIFY."; \
	 echo " *"; \
	 echo " * This file was generated by Kbuild"; \
	 echo " *"; \
	 echo " */"; \
	 echo ""; \
	 sed -ne $(sed-y) $<; \
	 echo ""; \
	 echo "#endif" ) > $@
endef

# We use internal kbuild rules to avoid the "is up to date" message from make
kernel/bounds.s: kernel/bounds.c FORCE
	$(Q)mkdir -p $(dir $@)
	$(call if_changed_dep,cc_s_c)

$(obj)/$(bounds-file): kernel/bounds.s Kbuild
	$(Q)mkdir -p $(dir $@)
	$(call cmd,bounds)

#####
# 2) Generate asm-offsets.h
#

offsets-file := include/generated/asm-offsets.h

always  += $(offsets-file)
targets += $(offsets-file)
targets += arch/$(SRCARCH)/kernel/asm-offsets.s


# Default sed regexp - multiline due to syntax constraints
define sed-y
	"/^->/{s:->#\(.*\):/* \1 */:; \
	s:^->\([^ ]*\) [\$$#]*\([-0-9]*\) \(.*\):#define \1 \2 /* \3 */:; \
	s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; \
	s:->::; p;}"
endef

quiet_cmd_offsets = GEN     $@
define cmd_offsets
	(set -e; \
	 echo "#ifndef __ASM_OFFSETS_H__"; \
	 echo "#define __ASM_OFFSETS_H__"; \
	 echo "/*"; \
	 echo " * DO NOT MODIFY."; \
	 echo " *"; \
	 echo " * This file was generated by Kbuild"; \
	 echo " *"; \
	 echo " */"; \
	 echo ""; \
	 sed -ne $(sed-y) $<; \
	 echo ""; \
	 echo "#endif" ) > $@
endef

# We use internal kbuild rules to avoid the "is up to date" message from make
arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
                                      $(obj)/$(bounds-file) FORCE
	$(Q)mkdir -p $(dir $@)
	$(call if_changed_dep,cc_s_c)

$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s Kbuild
	$(call cmd,offsets)

#####
# 3) Check for missing system calls
#

always += missing-syscalls
targets += missing-syscalls

quiet_cmd_syscalls = CALL    $<
      cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)

missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
	$(call cmd,syscalls)

# Keep these two files during make clean
no-clean-files := $(bounds-file) $(offsets-file)
back to top