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authorRussell Harmon via samba-technical <samba-technical@lists.samba.org>2023-08-10 10:19:22 +0300
committerSteve French <stfrench@microsoft.com>2023-08-14 16:39:12 +0300
commit69513dd669e243928f7450893190915a88f84a2b (patch)
tree556bdb7a2ba2ebbb1b84d0bdeb87c1a979f992d8 /scripts/gdb/linux/utils.py
parente8f5f849ffce24490eb9449e98312b66c0dba76f (diff)
downloadlinux-69513dd669e243928f7450893190915a88f84a2b.tar.xz
cifs: Release folio lock on fscache read hit.
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>
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