| Message ID | 166757987929.950645.12595273010425381286.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] netfs: Fix missing xas_retry() calls in xarray iteration | expand |
On 11/5/22 12:37 AM, David Howells wrote: > netfslib has a number of places in which it performs iteration of an xarray > whilst being under the RCU read lock. It *should* call xas_retry() as the > first thing inside of the loop and do "continue" if it returns true in case > the xarray walker passed out a special value indicating that the walk needs > to be redone from the root[*]. > > Fix this by adding the missing retry checks. > > [*] I wonder if this should be done inside xas_find(), xas_next_node() and > suchlike, but I'm told that's not an simple change to effect. > > This can cause an oops like that below. Note the faulting address - this > is an internal value (|0x2) returned from xarray. > > BUG: kernel NULL pointer dereference, address: 0000000000000402 > ... > RIP: 0010:netfs_rreq_unlock+0xef/0x380 [netfs] > ... > Call Trace: > netfs_rreq_assess+0xa6/0x240 [netfs] > netfs_readpage+0x173/0x3b0 [netfs] > ? init_wait_var_entry+0x50/0x50 > filemap_read_page+0x33/0xf0 > filemap_get_pages+0x2f2/0x3f0 > filemap_read+0xaa/0x320 > ? do_filp_open+0xb2/0x150 > ? rmqueue+0x3be/0xe10 > ceph_read_iter+0x1fe/0x680 [ceph] > ? new_sync_read+0x115/0x1a0 > new_sync_read+0x115/0x1a0 > vfs_read+0xf3/0x180 > ksys_read+0x5f/0xe0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers") > Reported-by: George Law <glaw@redhat.com> > Signed-off-by: David Howells <dhowells@redhat.com> > Reviewed-by: Jeff Layton <jlayton@kernel.org> > cc: Matthew Wilcox <willy@infradead.org> > cc: linux-cachefs@redhat.com > cc: linux-fsdevel@vger.kernel.org > --- Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c index 0ce535852151..baf668fb4315 100644 --- a/fs/netfs/buffered_read.c +++ b/fs/netfs/buffered_read.c @@ -46,10 +46,15 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq) rcu_read_lock(); xas_for_each(&xas, folio, last_page) { - unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE; - unsigned int pgend = pgpos + folio_size(folio); + unsigned int pgpos, pgend; bool pg_failed = false; + if (xas_retry(&xas, folio)) + continue; + + pgpos = (folio_index(folio) - start_page) * PAGE_SIZE; + pgend = pgpos + folio_size(folio); + for (;;) { if (!subreq) { pg_failed = true; diff --git a/fs/netfs/io.c b/fs/netfs/io.c index 428925899282..e374767d1b68 100644 --- a/fs/netfs/io.c +++ b/fs/netfs/io.c @@ -121,6 +121,9 @@ static void netfs_rreq_unmark_after_write(struct netfs_io_request *rreq, XA_STATE(xas, &rreq->mapping->i_pages, subreq->start / PAGE_SIZE); xas_for_each(&xas, folio, (subreq->start + subreq->len - 1) / PAGE_SIZE) { + if (xas_retry(&xas, folio)) + continue; + /* We might have multiple writes from the same huge * folio, but we mustn't unlock a folio more than once. */
netfslib has a number of places in which it performs iteration of an xarray whilst being under the RCU read lock. It *should* call xas_retry() as the first thing inside of the loop and do "continue" if it returns true in case the xarray walker passed out a special value indicating that the walk needs to be redone from the root[*]. Fix this by adding the missing retry checks. [*] I wonder if this should be done inside xas_find(), xas_next_node() and suchlike, but I'm told that's not an simple change to effect. This can cause an oops like that below. Note the faulting address - this is an internal value (|0x2) returned from xarray. BUG: kernel NULL pointer dereference, address: 0000000000000402 ... RIP: 0010:netfs_rreq_unlock+0xef/0x380 [netfs] ... Call Trace: netfs_rreq_assess+0xa6/0x240 [netfs] netfs_readpage+0x173/0x3b0 [netfs] ? init_wait_var_entry+0x50/0x50 filemap_read_page+0x33/0xf0 filemap_get_pages+0x2f2/0x3f0 filemap_read+0xaa/0x320 ? do_filp_open+0xb2/0x150 ? rmqueue+0x3be/0xe10 ceph_read_iter+0x1fe/0x680 [ceph] ? new_sync_read+0x115/0x1a0 new_sync_read+0x115/0x1a0 vfs_read+0xf3/0x180 ksys_read+0x5f/0xe0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers") Reported-by: George Law <glaw@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> cc: Matthew Wilcox <willy@infradead.org> cc: linux-cachefs@redhat.com cc: linux-fsdevel@vger.kernel.org --- fs/netfs/buffered_read.c | 9 +++++++-- fs/netfs/io.c | 3 +++ 2 files changed, 10 insertions(+), 2 deletions(-)