| Message ID | 20190719143222.16058-3-lhenriques@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Sleeping functions in invalid context bug fixes | expand |
On Fri, 2019-07-19 at 15:32 +0100, Luis Henriques wrote: > Calling ceph_buffer_put() in __ceph_setxattr() may end up freeing the > i_xattrs.prealloc_blob buffer while holding the i_ceph_lock. This can be > fixed by postponing the call until later, when the lock is released. > > The following backtrace was triggered by fstests generic/117. > > BUG: sleeping function called from invalid context at mm/vmalloc.c:2283 > in_atomic(): 1, irqs_disabled(): 0, pid: 650, name: fsstress > 3 locks held by fsstress/650: > #0: 00000000870a0fe8 (sb_writers#8){.+.+}, at: mnt_want_write+0x20/0x50 > #1: 00000000ba0c4c74 (&type->i_mutex_dir_key#6){++++}, at: vfs_setxattr+0x55/0xa0 > #2: 000000008dfbb3f2 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: __ceph_setxattr+0x297/0x810 > CPU: 1 PID: 650 Comm: fsstress Not tainted 5.2.0+ #437 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014 > Call Trace: > dump_stack+0x67/0x90 > ___might_sleep.cold+0x9f/0xb1 > vfree+0x4b/0x60 > ceph_buffer_release+0x1b/0x60 > __ceph_setxattr+0x2b4/0x810 > __vfs_setxattr+0x66/0x80 > __vfs_setxattr_noperm+0x59/0xf0 > vfs_setxattr+0x81/0xa0 > setxattr+0x115/0x230 > ? filename_lookup+0xc9/0x140 > ? rcu_read_lock_sched_held+0x74/0x80 > ? rcu_sync_lockdep_assert+0x2e/0x60 > ? __sb_start_write+0x142/0x1a0 > ? mnt_want_write+0x20/0x50 > path_setxattr+0xba/0xd0 > __x64_sys_lsetxattr+0x24/0x30 > do_syscall_64+0x50/0x1c0 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x7ff23514359a > > Signed-off-by: Luis Henriques <lhenriques@suse.com> > --- > fs/ceph/xattr.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c > index 37b458a9af3a..c083557b3657 100644 > --- a/fs/ceph/xattr.c > +++ b/fs/ceph/xattr.c > @@ -1036,6 +1036,7 @@ int __ceph_setxattr(struct inode *inode, const char *name, > struct ceph_inode_info *ci = ceph_inode(inode); > struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc; > struct ceph_cap_flush *prealloc_cf = NULL; > + struct ceph_buffer *old_blob = NULL; > int issued; > int err; > int dirty = 0; > @@ -1109,13 +1110,15 @@ int __ceph_setxattr(struct inode *inode, const char *name, > struct ceph_buffer *blob; > > spin_unlock(&ci->i_ceph_lock); > - dout(" preaallocating new blob size=%d\n", required_blob_size); > + ceph_buffer_put(old_blob); /* Shouldn't be required */ > + dout(" pre-allocating new blob size=%d\n", required_blob_size); > blob = ceph_buffer_new(required_blob_size, GFP_NOFS); > if (!blob) > goto do_sync_unlocked; > spin_lock(&ci->i_ceph_lock); > + /* prealloc_blob can't be released while holding i_ceph_lock */ > if (ci->i_xattrs.prealloc_blob) > - ceph_buffer_put(ci->i_xattrs.prealloc_blob); > + old_blob = ci->i_xattrs.prealloc_blob; > ci->i_xattrs.prealloc_blob = blob; > goto retry; > } > @@ -1131,6 +1134,7 @@ int __ceph_setxattr(struct inode *inode, const char *name, > } > > spin_unlock(&ci->i_ceph_lock); > + ceph_buffer_put(old_blob); > if (lock_snap_rwsem) > up_read(&mdsc->snap_rwsem); > if (dirty) (cc'ing Al) Al pointed out on IRC that vfree should be callable under spinlock. It only sleeps if !in_interrupt(), and I think that should return true if we're holding a spinlock. I'll plan to try replicating this soon.
On Fri, Jul 19, 2019 at 07:07:49PM -0400, Jeff Layton wrote: > Al pointed out on IRC that vfree should be callable under spinlock. Al had been near-terminally low on caffeine at the time, posted a retraction a few minutes later and went to grab some coffee... > It > only sleeps if !in_interrupt(), and I think that should return true if > we're holding a spinlock. It can be used from RCU callbacks and all such; it *can't* be used from under spinlock - on non-preempt builds there's no way to recognize that.
On Sat, Jul 20, 2019 at 12:23:08AM +0100, Al Viro wrote: > On Fri, Jul 19, 2019 at 07:07:49PM -0400, Jeff Layton wrote: > > > Al pointed out on IRC that vfree should be callable under spinlock. > > Al had been near-terminally low on caffeine at the time, posted > a retraction a few minutes later and went to grab some coffee... > > > It > > only sleeps if !in_interrupt(), and I think that should return true if > > we're holding a spinlock. > > It can be used from RCU callbacks and all such; it *can't* be used from > under spinlock - on non-preempt builds there's no way to recognize that. Re original patch: looks like the sane way to handle that. Alternatively, we could add kvfree_atomic() for use in such situations, but I rather doubt that it's a good idea - not unless you need to free something under a spinlock held over a large area, which is generally a bad idea to start with... Note that vfree_atomic() has only one caller in the entire tree, BTW.
On Sat, 2019-07-20 at 00:30 +0100, Al Viro wrote: > On Sat, Jul 20, 2019 at 12:23:08AM +0100, Al Viro wrote: > > On Fri, Jul 19, 2019 at 07:07:49PM -0400, Jeff Layton wrote: > > > > > Al pointed out on IRC that vfree should be callable under spinlock. > > > > Al had been near-terminally low on caffeine at the time, posted > > a retraction a few minutes later and went to grab some coffee... > > > > > It > > > only sleeps if !in_interrupt(), and I think that should return true if > > > we're holding a spinlock. > > > > It can be used from RCU callbacks and all such; it *can't* be used from > > under spinlock - on non-preempt builds there's no way to recognize that. > > Re original patch: looks like the sane way to handle that. > Alternatively, we could add kvfree_atomic() for use in such situations, > but I rather doubt that it's a good idea - not unless you need to free > something under a spinlock held over a large area, which is generally > a bad idea to start with... > > Note that vfree_atomic() has only one caller in the entire tree, > BTW. In that case, I wonder if we ought to add this to the top of kvfree(): might_sleep_if(!in_interrupt()); Might there be other places that are calling it under spinlock that are almost always going down the kfree() path?
diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c index 37b458a9af3a..c083557b3657 100644 --- a/fs/ceph/xattr.c +++ b/fs/ceph/xattr.c @@ -1036,6 +1036,7 @@ int __ceph_setxattr(struct inode *inode, const char *name, struct ceph_inode_info *ci = ceph_inode(inode); struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc; struct ceph_cap_flush *prealloc_cf = NULL; + struct ceph_buffer *old_blob = NULL; int issued; int err; int dirty = 0; @@ -1109,13 +1110,15 @@ int __ceph_setxattr(struct inode *inode, const char *name, struct ceph_buffer *blob; spin_unlock(&ci->i_ceph_lock); - dout(" preaallocating new blob size=%d\n", required_blob_size); + ceph_buffer_put(old_blob); /* Shouldn't be required */ + dout(" pre-allocating new blob size=%d\n", required_blob_size); blob = ceph_buffer_new(required_blob_size, GFP_NOFS); if (!blob) goto do_sync_unlocked; spin_lock(&ci->i_ceph_lock); + /* prealloc_blob can't be released while holding i_ceph_lock */ if (ci->i_xattrs.prealloc_blob) - ceph_buffer_put(ci->i_xattrs.prealloc_blob); + old_blob = ci->i_xattrs.prealloc_blob; ci->i_xattrs.prealloc_blob = blob; goto retry; } @@ -1131,6 +1134,7 @@ int __ceph_setxattr(struct inode *inode, const char *name, } spin_unlock(&ci->i_ceph_lock); + ceph_buffer_put(old_blob); if (lock_snap_rwsem) up_read(&mdsc->snap_rwsem); if (dirty)
Calling ceph_buffer_put() in __ceph_setxattr() may end up freeing the i_xattrs.prealloc_blob buffer while holding the i_ceph_lock. This can be fixed by postponing the call until later, when the lock is released. The following backtrace was triggered by fstests generic/117. BUG: sleeping function called from invalid context at mm/vmalloc.c:2283 in_atomic(): 1, irqs_disabled(): 0, pid: 650, name: fsstress 3 locks held by fsstress/650: #0: 00000000870a0fe8 (sb_writers#8){.+.+}, at: mnt_want_write+0x20/0x50 #1: 00000000ba0c4c74 (&type->i_mutex_dir_key#6){++++}, at: vfs_setxattr+0x55/0xa0 #2: 000000008dfbb3f2 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: __ceph_setxattr+0x297/0x810 CPU: 1 PID: 650 Comm: fsstress Not tainted 5.2.0+ #437 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack+0x67/0x90 ___might_sleep.cold+0x9f/0xb1 vfree+0x4b/0x60 ceph_buffer_release+0x1b/0x60 __ceph_setxattr+0x2b4/0x810 __vfs_setxattr+0x66/0x80 __vfs_setxattr_noperm+0x59/0xf0 vfs_setxattr+0x81/0xa0 setxattr+0x115/0x230 ? filename_lookup+0xc9/0x140 ? rcu_read_lock_sched_held+0x74/0x80 ? rcu_sync_lockdep_assert+0x2e/0x60 ? __sb_start_write+0x142/0x1a0 ? mnt_want_write+0x20/0x50 path_setxattr+0xba/0xd0 __x64_sys_lsetxattr+0x24/0x30 do_syscall_64+0x50/0x1c0 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7ff23514359a Signed-off-by: Luis Henriques <lhenriques@suse.com> --- fs/ceph/xattr.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)