From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Subject: mm: use down_read_killable for locking mmap_sem in access_remote_vm 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 <khlebnikov@xxxxxxxxxxxxxx> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx> Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memory.c | 4 +++- mm/nommu.c | 3 ++- 2 files changed, 5 insertions(+), 2 deletions(-) --- a/mm/memory.c~mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm +++ a/mm/memory.c @@ -4344,7 +4344,9 @@ int __access_remote_vm(struct task_struc 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; --- a/mm/nommu.c~mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm +++ a/mm/nommu.c @@ -1704,7 +1704,8 @@ int __access_remote_vm(struct task_struc 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); _
