From: Konstantin Khlebnikov <khlebni...@yandex-team.ru> [ Upstream commit 1e426fe28261b03f297992e89da3320b42816f4e ]
This function is used by ptrace and proc files like /proc/pid/cmdline and /proc/pid/environ. Access_remote_vm never returns error codes, all errors are ignored and only size of successfully read data is returned. So, if current task was killed we'll simply return 0 (bytes read). Mmap_sem could be locked for a long time or forever if something goes wrong. Using a killable lock permits cleanup of stuck tasks and simplifies investigation. Link: http://lkml.kernel.org/r/156007494202.3335.16782303099589302087.stgit@buzz Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru> Reviewed-by: Michal Koutný <mkou...@suse.com> Acked-by: Oleg Nesterov <o...@redhat.com> Acked-by: Michal Hocko <mho...@suse.com> Cc: Alexey Dobriyan <adobri...@gmail.com> Cc: Matthew Wilcox <wi...@infradead.org> Cc: Cyrill Gorcunov <gorcu...@gmail.com> Cc: Kirill Tkhai <ktk...@virtuozzo.com> Cc: Al Viro <v...@zeniv.linux.org.uk> Cc: Roman Gushchin <g...@fb.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Sasha Levin <sas...@kernel.org> --- mm/memory.c | 4 +++- mm/nommu.c | 3 ++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index ab650c21bccd..57402801ab09 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4260,7 +4260,9 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, void *old_buf = buf; int write = gup_flags & FOLL_WRITE; - down_read(&mm->mmap_sem); + if (down_read_killable(&mm->mmap_sem)) + return 0; + /* ignore errors, just check how much was successfully transferred */ while (len) { int bytes, ret, offset; diff --git a/mm/nommu.c b/mm/nommu.c index 749276beb109..1bd91ceadc82 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1777,7 +1777,8 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, struct vm_area_struct *vma; int write = gup_flags & FOLL_WRITE; - down_read(&mm->mmap_sem); + if (down_read_killable(&mm->mmap_sem)) + return 0; /* the access must start within one of the target process's mappings */ vma = find_vma(mm, addr); -- 2.20.1
