[PATCH] uml: fix hang on run_helper() failure on uml_net

Fix an hang on a pipe when run_helper() fails when called by change_tramp()
(i.e.  when calling uml_net) - reproduced the bug and verified this fixes it.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/um/drivers/net_user.c b/arch/um/drivers/net_user.c
index 0e2f06187ea7..0a7786e00cfb 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -182,7 +182,9 @@ static int change_tramp(char **argv, char *output, int output_len)
         pe_data.stdout = fds[1];
         pid = run_helper(change_pre_exec, &pe_data, argv, NULL);
 
-        read_output(fds[0], output, output_len);
+        if (pid > 0)    /* Avoid hang as we won't get data in failure case. */
+                read_output(fds[0], output, output_len);
+
         os_close_file(fds[0]);
         os_close_file(fds[1]);