When the buffer passed to a read or write system call is memory mapped to the same file, a page fault can occur in gfs2_fault. In that case, the task will already be holding the inode glock, and trying to take it again will result in a BUG in add_to_queue(). Fix that by recognizing the self-recursion case and either skipping the lock taking (when the glock is held in a compatible way), or fail the operation.

Likewise, a request to un-share a copy-on-write page can *probably* happen in similar situations, so treat the locking in gfs2_page_mkwrite in the same way.

A future patch will handle this case more gracefully, along with addressing more complex deadlock scenarios.

Reported-by: Jan Kara jack@suse.cz Fixes: 20f829999c38 ("gfs2: Rework read and page fault locking") Cc: stable@vger.kernel.org # v5.8+ Signed-off-by: Andreas Gruenbacher agruenba@redhat.com --- fs/gfs2/file.c | 40 ++++++++++++++++++++++++++++++---------- 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c index 6d77743f11a4..7d88abb4629b 100644 --- a/fs/gfs2/file.c +++ b/fs/gfs2/file.c @@ -423,6 +423,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf) struct page *page = vmf->page; struct inode *inode = file_inode(vmf->vma->vm_file); struct gfs2_inode *ip = GFS2_I(inode); + struct gfs2_holder *outer_gh = gfs2_glock_is_locked_by_me(ip->i_gl); struct gfs2_sbd *sdp = GFS2_SB(inode); struct gfs2_alloc_parms ap = { .aflags = 0, }; u64 offset = page_offset(page); @@ -436,10 +437,18 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf) sb_start_pagefault(inode->i_sb);

gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &gh); - err = gfs2_glock_nq(&gh); - if (err) { - ret = block_page_mkwrite_return(err); - goto out_uninit; + if (likely(!outer_gh)) { + err = gfs2_glock_nq(&gh); + if (err) { + ret = block_page_mkwrite_return(err); + goto out_uninit; + } + } else { + if (!gfs2_holder_is_compatible(outer_gh, LM_ST_EXCLUSIVE)) { + /* We could try to upgrade outer_gh here. */ + ret = VM_FAULT_SIGBUS; + goto out_uninit; + } }

/* Check page index against inode size */ @@ -540,7 +549,8 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf) out_quota_unlock: gfs2_quota_unlock(ip); out_unlock: - gfs2_glock_dq(&gh); + if (likely(!outer_gh)) + gfs2_glock_dq(&gh); out_uninit: gfs2_holder_uninit(&gh); if (ret == VM_FAULT_LOCKED) { @@ -555,6 +565,7 @@ static vm_fault_t gfs2_fault(struct vm_fault *vmf) { struct inode *inode = file_inode(vmf->vma->vm_file); struct gfs2_inode *ip = GFS2_I(inode); + struct gfs2_holder *outer_gh = gfs2_glock_is_locked_by_me(ip->i_gl); struct gfs2_holder gh; vm_fault_t ret; u16 state; @@ -562,13 +573,22 @@ static vm_fault_t gfs2_fault(struct vm_fault *vmf)

state = (vmf->flags & FAULT_FLAG_WRITE) ? LM_ST_EXCLUSIVE : LM_ST_SHARED; gfs2_holder_init(ip->i_gl, state, 0, &gh); - err = gfs2_glock_nq(&gh); - if (err) { - ret = block_page_mkwrite_return(err); - goto out_uninit; + if (likely(!outer_gh)) { + err = gfs2_glock_nq(&gh); + if (err) { + ret = block_page_mkwrite_return(err); + goto out_uninit; + } + } else { + if (!gfs2_holder_is_compatible(outer_gh, state)) { + /* We could try to upgrade outer_gh here. */ + ret = VM_FAULT_SIGBUS; + goto out_uninit; + } } ret = filemap_fault(vmf); - gfs2_glock_dq(&gh); + if (likely(!outer_gh)) + gfs2_glock_dq(&gh); out_uninit: gfs2_holder_uninit(&gh); return ret;