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 wrong. Killable lock allows to cleanup stuck tasks and simplifies investigation. Signed-off-by: Konstantin Khlebnikov <[email protected]> Reviewed-by: Michal Koutný <[email protected]> Acked-by: Oleg Nesterov <[email protected]> Acked-by: Michal Hocko <[email protected]> --- 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 ddf20bd0c317..9a4401d21e94 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4349,7 +4349,9 @@ 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 d8c02fbe03b5..b2823519f8cd 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1792,7 +1792,8 @@ 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);
