do_generic_file_read: s/EINTR/EIO/ if lock_page_killable() fails

If lock_page_killable() fails because the task was killed by SIGKILL or
any other fatal signal, do_generic_file_read() returns -EIO.

This seems to be OK, because in fact the userspace won't see this error,
the task will dequeue SIGKILL and exit.

However, /sbin/init is different, it will dequeue SIGKILL, ignore it, and
return to the user-space with the bogus -EIO.

Change the code to return the error code from lock_page_killable(), -EINTR.
This doesn't fix the bug, but perhaps makes sense anyway. Imho, with this
change the code looks a bit more logical, and the "good" init should handle
the spurious EINTR or short read.

Afaics we can also change lock_page_killable() to return -ERESTARTNOINTR,
but this can't prevent the short reads.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 7 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 876bc595d0f8..494ff20b6cfa 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1100,8 +1100,9 @@ page_ok:
 
 page_not_up_to_date:
                 /* Get exclusive access to the page ... */
-                if (lock_page_killable(page))
-                        goto readpage_eio;
+                error = lock_page_killable(page);
+                if (unlikely(error))
+                        goto readpage_error;
 
 page_not_up_to_date_locked:
                 /* Did it get truncated before we got the lock? */
@@ -1130,8 +1131,9 @@ readpage:
                 }
 
                 if (!PageUptodate(page)) {
-                        if (lock_page_killable(page))
-                                goto readpage_eio;
+                        error = lock_page_killable(page);
+                        if (unlikely(error))
+                                goto readpage_error;
                         if (!PageUptodate(page)) {
                                 if (page->mapping == NULL) {
                                         /*
@@ -1143,15 +1145,14 @@ readpage:
                                 }
                                 unlock_page(page);
                                 shrink_readahead_size_eio(filp, ra);
-                                goto readpage_eio;
+                                error = -EIO;
+                                goto readpage_error;
                         }
                         unlock_page(page);
                 }
 
                 goto page_ok;
 
-readpage_eio:
-                error = -EIO;
 readpage_error:
                 /* UHHUH! A synchronous read error occurred. Report it */
                 desc->error = error;