From 997778e332e9f6d3d1c42e9a222fcab8d4732c40 Mon Sep 17 00:00:00 2001
From: Michal Sekletar <msekleta@redhat.com>
Date: Fri, 27 May 2016 14:29:17 +0200
Subject: [PATCH] readahead: do not increase nr_requests for root fs block
 device

Having nr_requests can cause system lockups. Arguably, this should get
fixed somehow in kernel. For now we just stop changing the
value.

Note that not bumping a value may cause that posix_fadvise call
will block in case there is no room in a request queue.

See: http://article.gmane.org/gmane.linux.kernel/1072356

RHEL-only
Resolves: #1314559
---
 src/readahead/readahead-common.c | 64 ----------------------------------------
 src/readahead/readahead-common.h |  2 --
 src/readahead/readahead-replay.c |  2 --
 3 files changed, 68 deletions(-)

diff --git a/src/readahead/readahead-common.c b/src/readahead/readahead-common.c
index 3ca48a7..6cf33f7 100644
--- a/src/readahead/readahead-common.c
+++ b/src/readahead/readahead-common.c
@@ -253,70 +253,6 @@ ReadaheadShared *shared_get(void) {
         return m;
 }
 
-/* We use 20K instead of the more human digestable 16K here. Why?
-   Simply so that it is more unlikely that users end up picking this
-   value too so that we can recognize better whether the user changed
-   the value while we had it temporarily bumped. */
-#define BUMP_REQUEST_NR (20*1024u)
-
-int block_bump_request_nr(const char *p) {
-        struct stat st;
-        uint64_t u;
-        char *ap = NULL, *line = NULL;
-        int r;
-        dev_t d;
-
-        assert(p);
-
-        if (stat(p, &st) < 0)
-                return -errno;
-
-        if (major(st.st_dev) == 0)
-                return 0;
-
-        d = st.st_dev;
-        block_get_whole_disk(d, &d);
-
-        if (asprintf(&ap, "/sys/dev/block/%u:%u/queue/nr_requests", major(d), minor(d)) < 0) {
-                r= -ENOMEM;
-                goto finish;
-        }
-
-        r = read_one_line_file(ap, &line);
-        if (r < 0) {
-                if (r == -ENOENT)
-                        r = 0;
-                goto finish;
-        }
-
-        r = safe_atou64(line, &u);
-        if (r >= 0 && u >= BUMP_REQUEST_NR) {
-                r = 0;
-                goto finish;
-        }
-
-        free(line);
-        line = NULL;
-
-        if (asprintf(&line, "%u", BUMP_REQUEST_NR) < 0) {
-                r = -ENOMEM;
-                goto finish;
-        }
-
-        r = write_string_file(ap, line);
-        if (r < 0)
-                goto finish;
-
-        log_info("Bumped block_nr parameter of %u:%u to %u. This is a temporary hack and should be removed one day.", major(d), minor(d), BUMP_REQUEST_NR);
-        r = 1;
-
-finish:
-        free(ap);
-        free(line);
-
-        return r;
-}
-
 int block_get_readahead(const char *p, uint64_t *bytes) {
         struct stat st;
         char *ap = NULL, *line = NULL;
diff --git a/src/readahead/readahead-common.h b/src/readahead/readahead-common.h
index b34f3aa..cc2ea81 100644
--- a/src/readahead/readahead-common.h
+++ b/src/readahead/readahead-common.h
@@ -51,8 +51,6 @@ typedef struct ReadaheadShared {
 
 ReadaheadShared *shared_get(void);
 
-int block_bump_request_nr(const char *p);
-
 int block_get_readahead(const char *p, uint64_t *bytes);
 int block_set_readahead(const char *p, uint64_t bytes);
 
diff --git a/src/readahead/readahead-replay.c b/src/readahead/readahead-replay.c
index f81e0fe..c2e2816 100644
--- a/src/readahead/readahead-replay.c
+++ b/src/readahead/readahead-replay.c
@@ -134,8 +134,6 @@ static int replay(const char *root) {
 
         assert(root);
 
-        block_bump_request_nr(root);
-
         if (asprintf(&pack_fn, "%s/.readahead", root) < 0)
                 return log_oom();