[GFS2] Fix page lock/glock deadlock

This fixes a race between the glock and the page lock encountered
during truncate in gfs2_readpage and gfs2_prepare_write. The gfs2_readpages
function doesn't need the same fix since it only uses a try lock anyway, so
it will fail back to gfs2_readpage in the case of a potential deadlock.

This bug was spotted by Russell Cattelan.

Cc: Russell Cattelan <cattelan@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 5c3962c80e88..3822189454a3 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -230,7 +230,7 @@ static int gfs2_readpage(struct file *file, struct page *page)
                                 /* gfs2_sharewrite_nopage has grabbed the ip->i_gl already */
                                 goto skip_lock;
                 }
-                gfs2_holder_init(ip->i_gl, LM_ST_SHARED, GL_ATIME|GL_AOP, &gh);
+                gfs2_holder_init(ip->i_gl, LM_ST_SHARED, GL_ATIME|LM_FLAG_TRY_1CB, &gh);
                 do_unlock = 1;
                 error = gfs2_glock_nq_m_atime(1, &gh);
                 if (unlikely(error))
@@ -254,6 +254,8 @@ skip_lock:
 out:
         return error;
 out_unlock:
+        if (error == GLR_TRYFAILED)
+                error = AOP_TRUNCATED_PAGE;
         unlock_page(page);
         if (do_unlock)
                 gfs2_holder_uninit(&gh);
@@ -293,7 +295,7 @@ static int gfs2_readpages(struct file *file, struct address_space *mapping,
                                 goto skip_lock;
                 }
                 gfs2_holder_init(ip->i_gl, LM_ST_SHARED,
-                                 LM_FLAG_TRY_1CB|GL_ATIME|GL_AOP, &gh);
+                                 LM_FLAG_TRY_1CB|GL_ATIME, &gh);
                 do_unlock = 1;
                 ret = gfs2_glock_nq_m_atime(1, &gh);
                 if (ret == GLR_TRYFAILED)
@@ -366,10 +368,13 @@ static int gfs2_prepare_write(struct file *file, struct page *page,
         unsigned int write_len = to - from;
 
 
-        gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ATIME|GL_AOP, &ip->i_gh);
+        gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ATIME|LM_FLAG_TRY_1CB, &ip->i_gh);
         error = gfs2_glock_nq_m_atime(1, &ip->i_gh);
-        if (error)
+        if (unlikely(error)) {
+                if (error == GLR_TRYFAILED)
+                        error = AOP_TRUNCATED_PAGE;
                 goto out_uninit;
+        }
 
         gfs2_write_calc_reserv(ip, write_len, &data_blocks, &ind_blocks);