tee: not checking for EAGAIN or EWOULDBLOCK causing missing output to terminal

[Austen W Lauria]

Hi all,

I see that this issue was reported prior in the mailing list, but just
wanted to bring it back to attention.

Customers have seen problems running our apps that produce a ton of output
(such mpirun that just dumps standard out) when using tee. The file gets
completely written to, but the output to the terminal is cut short. And
this appears to me to be an issue
where tee is not checking for EAGAIN in the fwrite() and read() call.

For example:

$. mpirun -np 5 ./stdout.exe 1000000 2>&1
| /smpi_dev/awlauria/coreutils/usr/bin/tee sten_out

Will produce about about 5 million lines of stdout (per 1 million per
process). Intermittently, not all output will be returned to the users
terminal. And when mpirun exits first in this case, the user will also be
greeted with a "tee: write error" message - probably because mpirun closed
the stdout/stderr on exit while tee was still running. If I modify mpirun
to just hang and not exit, tee will hang to infinity in the tee_files()
call (can see using pstack).

Using strace, I was able to narrow the failure to an EAGAIN on fwrite() in
tee:

write(1, "\nPrint to stdout line 13721 a mu"..., 1290) = -1 EAGAIN
(Resource temporarily unavailable) <--- The user program output.
write(2, "tee: ", 5)                    = -1 EAGAIN (Resource temporarily
unavailable)
write(2, "standard output", 15)         = -1 EAGAIN (Resource temporarily
unavailable)

I have a proposed patch here that solves the issue for us - I verified on
coreutils master. Can you take a look and provide some feedback? Thanks!

diff --git a/src/tee.c b/src/tee.c
index d3aecc7..13b4baf 100644
--- a/src/tee.c
+++ b/src/tee.c
@@ -229,19 +229,30 @@ tee_files (int nfiles, char **files)
   while (n_outputs)
     {
       bytes_read = read (STDIN_FILENO, buffer, sizeof buffer);
-      if (bytes_read < 0 && errno == EINTR)
+      if (bytes_read < 0
+          && (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK))
{
         continue;
+      }
+
       if (bytes_read <= 0)
         break;

       /* Write to all NFILES + 1 descriptors.
          Standard output is the first one.  */
-      for (i = 0; i <= nfiles; i++)
+      i = 0;
+      while (i <= nfiles) {
         if (descriptors[i]
             && fwrite (buffer, bytes_read, 1, descriptors[i]) != 1)
           {
             int w_errno = errno;
-            bool fail = errno != EPIPE || (output_error ==
output_error_exit
+            if(w_errno == EAGAIN || w_errno == EINTR || w_errno ==
EWOULDBLOCK) {
+              if(descriptors[i] == stdout) {
+                clearerr (stdout); /* Avoid redundant close_stdout
diagnostic.  */
+              }
+              continue;
+            }
+
+            bool fail = (errno != EPIPE)|| (output_error ==
output_error_exit
                                           || output_error ==
output_error_warn);
             if (descriptors[i] == stdout)
               clearerr (stdout); /* Avoid redundant close_stdout
diagnostic.  */
@@ -256,6 +267,8 @@ tee_files (int nfiles, char **files)
               ok = false;
             n_outputs--;
           }
+          i++;
+      }
     }

   if (bytes_read == -1)