pipe: set lower and upper limit on max pages in the pipe page array

We need at least two to guarantee proper POSIX behaviour, so
never allow a smaller limit than that.

Also expose a /proc/sys/fs/pipe-max-pages sysctl file that allows
root to define a sane upper limit. Make it default to 16 times the
default size, which is 16 pages.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8686b0f5fc12..c649d1c5fe09 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -52,6 +52,7 @@
 #include <linux/slow-work.h>
 #include <linux/perf_event.h>
 #include <linux/kprobes.h>
+#include <linux/pipe_fs_i.h>
 
 #include <asm/uaccess.h>
 #include <asm/processor.h>
@@ -1423,6 +1424,14 @@ static struct ctl_table fs_table[] = {
                 .child          = binfmt_misc_table,
         },
 #endif
+        {
+                .procname       = "pipe-max-pages",
+                .data           = &pipe_max_pages,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .extra1         = &two,
+        },
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt