4.17-stable review patch. If anyone has any objections, please let me know.
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From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp
[ Upstream commit 655c79bb40a0870adcd0871057d01de11625882b ]
As a theoretical problem, dup_mmap() of an mm_struct with 60000+ vmas can loop while potentially allocating memory, with mm->mmap_sem held for write by current thread. This is bad if current thread was selected as an OOM victim, for current thread will continue allocations using memory reserves while OOM reaper is unable to reclaim memory.
As an actually observable problem, it is not difficult to make OOM reaper unable to reclaim memory if the OOM victim is blocked at i_mmap_lock_write() in this loop. Unfortunately, since nobody can explain whether it is safe to use killable wait there, let's check for SIGKILL before trying to allocate memory. Even without an OOM event, there is no point with continuing the loop from the beginning if current thread is killed.
I tested with debug printk(). This patch should be safe because we already fail if security_vm_enough_memory_mm() or kmem_cache_alloc(GFP_KERNEL) fails and exit_mmap() handles it.
***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting exit_mmap() due to NULL mmap *****
[akpm@linux-foundation.org: add comment] Link: http://lkml.kernel.org/r/201804071938.CDE04681.SOFVQJFtMHOOLF@I-love.SAKURA.... Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Rik van Riel riel@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: David Rientjes rientjes@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/fork.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/kernel/fork.c +++ b/kernel/fork.c @@ -440,6 +440,14 @@ static __latent_entropy int dup_mmap(str continue; } charge = 0; + /* + * Don't duplicate many vmas if we've been oom-killed (for + * example) + */ + if (fatal_signal_pending(current)) { + retval = -EINTR; + goto out; + } if (mpnt->vm_flags & VM_ACCOUNT) { unsigned long len = vma_pages(mpnt);