The kernel is not required to act on fadvise, so fail silently
and ignore advice as long as it has a valid descriptor and
parameters.

Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Wong <redacted>
---

 Of course I wouldn't knowingly call posix_fadvise() on a file in
 tmpfs, but a userspace app often doesn't know (nor should it
 care) what type of filesystem it's on.

 I encountered EINVAL while running the Ruby 1.9.3 test suite on a
 stock Debian wheezy installation.  Wheezy uses tmpfs for "/tmp" by
 default and the test suite creates a temporary file to test the
 Ruby wrapper for posix_fadvise() on.

 mm/fadvise.c |   19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 469491e0..f9e48dd 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c

@@ -43,13 +43,13 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)

               goto out;
       }

-       mapping = file->f_mapping;
-       if (!mapping || len < 0) {
+       if (len < 0) {

@@ -93,10 +93,9 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)

               spin_unlock(&file->f_lock);
               break;
       case POSIX_FADV_WILLNEED:
-               if (!mapping->a_ops->readpage) {
-                       ret = -EINVAL;
+               /* ignore the advice if readahead isn't possible (tmpfs) */
+               if (!mapping->a_ops->readpage)
                       break;
-               }

               /* First and last PARTIAL page! */
               start_index = offset >> PAGE_CACHE_SHIFT;

@@ -106,12 +105,8 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)

               nrpages = end_index - start_index + 1;
               if (!nrpages)
                       nrpages = ~0UL;
-
-               ret = force_page_cache_readahead(mapping, file,
-                               start_index,
-                               nrpages);
-               if (ret > 0)
-                       ret = 0;
+
+               force_page_cache_readahead(mapping, file, start_index, nrpages);
               break;
       case POSIX_FADV_NOREUSE:
               break;
--
Eric Wong
--
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