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H A D | locks.c | diff 19e729a928172103e101ffd0829fd13e68c13f78 Mon Apr 14 21:03:02 CEST 2008 J. Bruce Fields <bfields@citi.umich.edu> locks: fix possible infinite loop in fcntl(F_SETLKW) over nfs
Miklos Szeredi found the bug:
"Basically what happens is that on the server nlm_fopen() calls nfsd_open() which returns -EACCES, to which nlm_fopen() returns NLM_LCK_DENIED.
"On the client this will turn into a -EAGAIN (nlm_stat_to_errno()), which in will cause fcntl_setlk() to retry forever."
So, for example, opening a file on an nfs filesystem, changing permissions to forbid further access, then trying to lock the file, could result in an infinite loop.
And Trond Myklebust identified the culprit, from Marc Eshel and I:
7723ec9777d9832849b76475b1a21a2872a40d20 "locks: factor out generic/filesystem switch from setlock code"
That commit claimed to just be reshuffling code, but actually introduced a behavioral change by calling the lock method repeatedly as long as it returned -EAGAIN.
We assumed this would be safe, since we assumed a lock of type SETLKW would only return with either success or an error other than -EAGAIN. However, nfs does can in fact return -EAGAIN in this situation, and independently of whether that behavior is correct or not, we don't actually need this change, and it seems far safer not to depend on such assumptions about the filesystem's ->lock method.
Therefore, revert the problematic part of the original commit. This leaves vfs_lock_file() and its other callers unchanged, while returning fcntl_setlk and fcntl_setlk64 to their former behavior.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu> Tested-by: Miklos Szeredi <mszeredi@suse.cz> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Cc: Marc Eshel <eshel@almaden.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 7723ec9777d9832849b76475b1a21a2872a40d20 Thu Jan 18 21:08:55 CET 2007 Marc Eshel <eshel@almaden.ibm.com> locks: factor out generic/filesystem switch from setlock code
Factor out the code that switches between generic and filesystem-specific lock methods; eventually we want to call this from lock managers (lockd and nfsd) too; currently they only call the generic methods.
This patch does that for all the setlk code.
Signed-off-by: Marc Eshel <eshel@almaden.ibm.com> Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
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