From 9b22b0b726c6e46048767728a0900c8c05f93c21 Mon Sep 17 00:00:00 2001 From: Steve French Date: Tue, 2 Oct 2007 01:11:08 +0000 Subject: [PATCH] [CIFS] Reduce chance of list corruption in find_writable_file When find_writable_file is racing with close and the session to the server goes down, Shaggy noticed that there was a chance that an open file in the list of files off the inode could have been freed by close since cifs_reconnect can block (the spinlock thus not held). This means that we have to start over at the beginning of the list in some cases. There is a 2nd change that needs to be made later (pointed out by Jeremy Allison and Shaggy) in order to prevent cifs_close ever freeing the cifs per file info when a write is pending. Although we delay close from freeing this memory for sufficiently long for all known cases, ultimately on a very, very slow write overlapping a close pending we need to allow close to return (without freeing the cifs file info) and defer freeing the memory to be the responsibility of the (sloooow) write thread (presumably have to look at every place wrtPending is decremented - and add a flag for deferred free for after wrtPending goes to zero). Acked-by: Shaggy Acked-by: Shirish Pargaonkar Signed-off-by: Steve French --- fs/cifs/file.c | 54 ++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 39 insertions(+), 15 deletions(-) diff --git a/fs/cifs/file.c b/fs/cifs/file.c index 7925491938..780c0e3e47 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -1042,6 +1042,7 @@ struct cifsFileInfo *find_writable_file(struct cifsInodeInfo *cifs_inode) } read_lock(&GlobalSMBSeslock); +refind_writable: list_for_each_entry(open_file, &cifs_inode->openFileList, flist) { if (open_file->closePend) continue; @@ -1049,26 +1050,49 @@ struct cifsFileInfo *find_writable_file(struct cifsInodeInfo *cifs_inode) ((open_file->pfile->f_flags & O_RDWR) || (open_file->pfile->f_flags & O_WRONLY))) { atomic_inc(&open_file->wrtPending); + + if (!open_file->invalidHandle) { + /* found a good writable file */ + read_unlock(&GlobalSMBSeslock); + return open_file; + } + read_unlock(&GlobalSMBSeslock); - if (open_file->invalidHandle) { - rc = cifs_reopen_file(open_file->pfile, FALSE); - /* if it fails, try another handle - might be */ - /* dangerous to hold up writepages with retry */ - if (rc) { - cFYI(1, ("wp failed on reopen file")); + /* Had to unlock since following call can block */ + rc = cifs_reopen_file(open_file->pfile, FALSE); + if (!rc) { + if (!open_file->closePend) + return open_file; + else { /* start over in case this was deleted */ + /* since the list could be modified */ read_lock(&GlobalSMBSeslock); - /* can not use this handle, no write - pending on this one after all */ atomic_dec(&open_file->wrtPending); - continue; + goto refind_writable; } } - if (open_file->closePend) { - read_lock(&GlobalSMBSeslock); - atomic_dec(&open_file->wrtPending); - continue; - } - return open_file; + + /* if it fails, try another handle if possible - + (we can not do this if closePending since + loop could be modified - in which case we + have to start at the beginning of the list + again. Note that it would be bad + to hold up writepages here (rather than + in caller) with continuous retries */ + cFYI(1, ("wp failed on reopen file")); + read_lock(&GlobalSMBSeslock); + /* can not use this handle, no write + pending on this one after all */ + atomic_dec(&open_file->wrtPending); + + if (open_file->closePend) /* list could have changed */ + goto refind_writable; + /* else we simply continue to the next entry. Thus + we do not loop on reopen errors. If we + can not reopen the file, for example if we + reconnected to a server with another client + racing to delete or lock the file we would not + make progress if we restarted before the beginning + of the loop here. */ } } read_unlock(&GlobalSMBSeslock); -- 2.39.5