https://github.com/torvalds/linux
Revision 31a78f23bac0069004e69f98808b6988baccb6b6 authored by Balbir Singh on 28 September 2008, 22:09:31 UTC, committed by Linus Torvalds on 29 September 2008, 15:41:47 UTC
There's a race between mm->owner assignment and swapoff, more easily seen when task slab poisoning is turned on. The condition occurs when try_to_unuse() runs in parallel with an exiting task. A similar race can occur with callers of get_task_mm(), such as /proc/<pid>/<mmstats> or ptrace or page migration. CPU0 CPU1 try_to_unuse looks at mm = task0->mm increments mm->mm_users task 0 exits mm->owner needs to be updated, but no new owner is found (mm_users > 1, but no other task has task->mm = task0->mm) mm_update_next_owner() leaves mmput(mm) decrements mm->mm_users task0 freed dereferencing mm->owner fails The fix is to notify the subsystem via mm_owner_changed callback(), if no new owner is found, by specifying the new task as NULL. Jiri Slaby: mm->owner was set to NULL prior to calling cgroup_mm_owner_callbacks(), but must be set after that, so as not to pass NULL as old owner causing oops. Daisuke Nishimura: mm_update_next_owner() may set mm->owner to NULL, but mem_cgroup_from_task() and its callers need to take account of this situation to avoid oops. Hugh Dickins: Lockdep warning and hang below exec_mmap() when testing these patches. exit_mm() up_reads mmap_sem before calling mm_update_next_owner(), so exec_mmap() now needs to do the same. And with that repositioning, there's now no point in mm_need_new_owner() allowing for NULL mm. Reported-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com> Signed-off-by: Jiri Slaby <jirislaby@gmail.com> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent bf5cb66
Tip revision: 31a78f23bac0069004e69f98808b6988baccb6b6 authored by Balbir Singh on 28 September 2008, 22:09:31 UTC
mm owner: fix race between swapoff and exit
mm owner: fix race between swapoff and exit
Tip revision: 31a78f2
File | Mode | Size |
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Documentation | ||
arch | ||
block | ||
crypto | ||
drivers | ||
firmware | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
usr | ||
virt | ||
.gitignore | -rw-r--r-- | 867 bytes |
.mailmap | -rw-r--r-- | 3.7 KB |
COPYING | -rw-r--r-- | 18.3 KB |
CREDITS | -rw-r--r-- | 90.7 KB |
Kbuild | -rw-r--r-- | 2.4 KB |
MAINTAINERS | -rw-r--r-- | 99.5 KB |
Makefile | -rw-r--r-- | 55.4 KB |
README | -rw-r--r-- | 16.5 KB |
REPORTING-BUGS | -rw-r--r-- | 3.1 KB |
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