4.19-stable review patch. If anyone has any objections, please let me know.
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From: Russell Harmon via samba-technical samba-technical@lists.samba.org
commit 69513dd669e243928f7450893190915a88f84a2b upstream.
Under the current code, when cifs_readpage_worker is called, the call contract is that the callee should unlock the page. This is documented in the read_folio section of Documentation/filesystems/vfs.rst as:
The filesystem should unlock the folio once the read has completed, whether it was successful or not.
Without this change, when fscache is in use and cache hit occurs during a read, the page lock is leaked, producing the following stack on subsequent reads (via mmap) to the page:
$ cat /proc/3890/task/12864/stack [<0>] folio_wait_bit_common+0x124/0x350 [<0>] filemap_read_folio+0xad/0xf0 [<0>] filemap_fault+0x8b1/0xab0 [<0>] __do_fault+0x39/0x150 [<0>] do_fault+0x25c/0x3e0 [<0>] __handle_mm_fault+0x6ca/0xc70 [<0>] handle_mm_fault+0xe9/0x350 [<0>] do_user_addr_fault+0x225/0x6c0 [<0>] exc_page_fault+0x84/0x1b0 [<0>] asm_exc_page_fault+0x27/0x30
This requires a reboot to resolve; it is a deadlock.
Note however that the call to cifs_readpage_from_fscache does mark the page clean, but does not free the folio lock. This happens in __cifs_readpage_from_fscache on success. Releasing the lock at that point however is not appropriate as cifs_readahead also calls cifs_readpage_from_fscache and *does* unconditionally release the lock after its return. This change therefore effectively makes cifs_readpage_worker work like cifs_readahead.
Signed-off-by: Russell Harmon russ@har.mn Acked-by: Paulo Alcantara (SUSE) pc@manguebit.com Reviewed-by: David Howells dhowells@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/cifs/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -3991,9 +3991,9 @@ static int cifs_readpage_worker(struct f
io_error: kunmap(page); - unlock_page(page);
read_complete: + unlock_page(page); return rc; }