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authorDavid Woodhouse <David.Woodhouse@intel.com>2016-02-01 15:37:20 +0300
committerDavid Woodhouse <David.Woodhouse@intel.com>2016-02-25 14:11:26 +0300
commit49e91e7079febe59a20ca885a87dd1c54240d0f1 (patch)
tree492560579a27a7658d2327f0e0a3a6eb825a303f /fs/jffs2/gc.c
parent157078f64b8a9cd7011b6b900b2f2498df850748 (diff)
downloadlinux-49e91e7079febe59a20ca885a87dd1c54240d0f1.tar.xz
jffs2: Fix page lock / f->sem deadlock
With this fix, all code paths should now be obtaining the page lock before f->sem. Reported-by: Szabó Tamás <sztomi89@gmail.com> Tested-by: Thomas Betker <thomas.betker@rohde-schwarz.com> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'fs/jffs2/gc.c')
-rw-r--r--fs/jffs2/gc.c17
1 files changed, 10 insertions, 7 deletions
diff --git a/fs/jffs2/gc.c b/fs/jffs2/gc.c
index 5a2dec2b064c..95d5880a63ee 100644
--- a/fs/jffs2/gc.c
+++ b/fs/jffs2/gc.c
@@ -1296,14 +1296,17 @@ static int jffs2_garbage_collect_dnode(struct jffs2_sb_info *c, struct jffs2_era
BUG_ON(start > orig_start);
}
- /* First, use readpage() to read the appropriate page into the page cache */
- /* Q: What happens if we actually try to GC the _same_ page for which commit_write()
- * triggered garbage collection in the first place?
- * A: I _think_ it's OK. read_cache_page shouldn't deadlock, we'll write out the
- * page OK. We'll actually write it out again in commit_write, which is a little
- * suboptimal, but at least we're correct.
- */
+ /* The rules state that we must obtain the page lock *before* f->sem, so
+ * drop f->sem temporarily. Since we also hold c->alloc_sem, nothing's
+ * actually going to *change* so we're safe; we only allow reading.
+ *
+ * It is important to note that jffs2_write_begin() will ensure that its
+ * page is marked Uptodate before allocating space. That means that if we
+ * end up here trying to GC the *same* page that jffs2_write_begin() is
+ * trying to write out, read_cache_page() will not deadlock. */
+ mutex_unlock(&f->sem);
pg_ptr = jffs2_gc_fetch_page(c, f, start, &pg);
+ mutex_lock(&f->sem);
if (IS_ERR(pg_ptr)) {
pr_warn("read_cache_page() returned error: %ld\n",