kernel/git/stable/linux.git/fs/buffer.c, branch linux-2.6.29.y

mm: close page_mkwrite races

2009-05-18T23:35:04+00:00

commit b827e496c893de0c0f142abfaeb8730a2fd6b37f upstream. Change page_mkwrite to allow implementations to return with the page locked, and also change it's callers (in page fault paths) to hold the lock until the page is marked dirty. This allows the filesystem to have full control of page dirtying events coming from the VM. Rather than simply hold the page locked over the page_mkwrite call, we call page_mkwrite with the page unlocked and allow callers to return with it locked, so filesystems can avoid LOR conditions with page lock. The problem with the current scheme is this: a filesystem that wants to associate some metadata with a page as long as the page is dirty, will perform this manipulation in its ->page_mkwrite. It currently then must return with the page unlocked and may not hold any other locks (according to existing page_mkwrite convention). In this window, the VM could write out the page, clearing page-dirty. The filesystem has no good way to detect that a dirty pte is about to be attached, so it will happily write out the page, at which point, the filesystem may manipulate the metadata to reflect that the page is no longer dirty. It is not always possible to perform the required metadata manipulation in ->set_page_dirty, because that function cannot block or fail. The filesystem may need to allocate some data structure, for example. And the VM cannot mark the pte dirty before page_mkwrite, because page_mkwrite is allowed to fail, so we must not allow any window where the page could be written to if page_mkwrite does fail. This solution of holding the page locked over the 3 critical operations (page_mkwrite, setting the pte dirty, and finally setting the page dirty) closes out races nicely, preventing page cleaning for writeout being initiated in that window. This provides the filesystem with a strong synchronisation against the VM here. - Sage needs this race closed for ceph filesystem. - Trond for NFS (http://bugzilla.kernel.org/show_bug.cgi?id=12913). - I need it for fsblock. - I suspect other filesystems may need it too (eg. btrfs). - I have converted buffer.c to the new locking. Even simple block allocation under dirty pages might be susceptible to i_size changing under partial page at the end of file (we also have a buffer.c-side problem here, but it cannot be fixed properly without this patch). - Other filesystems (eg. NFS, maybe btrfs) will need to change their page_mkwrite functions themselves. [ This also moves page_mkwrite another step closer to fault, which should eventually allow page_mkwrite to be moved into ->fault, and thus avoiding a filesystem calldown and page lock/unlock cycle in __do_fault. ] [akpm@linux-foundation.org: fix derefs of NULL ->mapping] Cc: Sage Weil Cc: Trond Myklebust Signed-off-by: Nick Piggin Cc: Valdis Kletnieks Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

fs: fix page_mkwrite error cases in core code and btrfs

2009-05-18T23:35:03+00:00

commit 56a76f8275c379ed73c8a43cfa1dfa2f5e9cfa19 upstream. page_mkwrite is called with neither the page lock nor the ptl held. This means a page can be concurrently truncated or invalidated out from underneath it. Callers are supposed to prevent truncate races themselves, however previously the only thing they can do in case they hit one is to raise a SIGBUS. A sigbus is wrong for the case that the page has been invalidated or truncated within i_size (eg. hole punched). Callers may also have to perform memory allocations in this path, where again, SIGBUS would be wrong. The previous patch ("mm: page_mkwrite change prototype to match fault") made it possible to properly specify errors. Convert the generic buffer.c code and btrfs to return sane error values (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the fault handler to exit without doing anything, and the fault will be retried properly). This fixes core code, and converts btrfs as a template/example. All other filesystems defining their own page_mkwrite should be fixed in a similar manner. Acked-by: Chris Mason Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mm: page_mkwrite change prototype to match fault

2009-05-18T23:35:02+00:00

commit c2ec175c39f62949438354f603f4aa170846aabb upstream. Change the page_mkwrite prototype to take a struct vm_fault, and return VM_FAULT_xxx flags. There should be no functional change. This makes it possible to return much more detailed error information to the VM (and also can provide more information eg. virtual_address to the driver, which might be important in some special cases). This is required for a subsequent fix. And will also make it easier to merge page_mkwrite() with fault() in future. Signed-off-by: Nick Piggin Cc: Chris Mason Cc: Trond Myklebust Cc: Miklos Szeredi Cc: Steven Whitehouse Cc: Mark Fasheh Cc: Joel Becker Cc: Artem Bityutskiy Cc: Felix Blyakher Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

Fix race in create_empty_buffers() vs __set_page_dirty_buffers()

2009-03-19T18:32:05+00:00

Nick Piggin noticed this (very unlikely) race between setting a page dirty and creating the buffers for it - we need to hold the mapping private_lock until we've set the page dirty bit in order to make sure that create_empty_buffers() might not build up a set of buffers without the dirty bits set when the page is dirty. I doubt anybody has ever hit this race (and it didn't solve the issue Nick was looking at), but as Nick says: "Still, it does appear to solve a real race, which we should close." Acked-by: Nick Piggin Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.dk/linux-2.6-block

2009-02-19T02:33:04+00:00

* 'for-linus' of git://git.kernel.dk/linux-2.6-block: block: fix deadlock in blk_abort_queue() for drivers that readd to timeout list block: fix booting from partitioned md array block: revert part of 18ce3751ccd488c78d3827e9f6bf54e6322676fb cciss: PCI power management reset for kexec paride/pg.c: xs(): &&/|| confusion fs/bio: bio_alloc_bioset: pass right object ptr to mempool_free block: fix bad definition of BIO_RW_SYNC bsg: Fix sense buffer bug in SG_IO

mm: task dirty accounting fix

2009-02-18T23:37:54+00:00

YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty). Additionally, there is some inconsistency about when task_dirty_inc is called. It is used for dirty balancing, however it even gets called for __set_page_dirty_no_writeback. So rather than increment it in a set_page_dirty wrapper, move it down to exactly where the dirty page accounting stats are incremented. Cc: YAMAMOTO Takashi Signed-off-by: Nick Piggin Acked-by: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

block: revert part of 18ce3751ccd488c78d3827e9f6bf54e6322676fb

2009-02-18T09:32:01+00:00

The above commit added WRITE_SYNC and switched various places to using that for committing writes that will be waited upon immediately after submission. However, this causes a performance regression with AS and CFQ for ext3 at least, since sync_dirty_buffer() will submit some writes with WRITE_SYNC while ext3 has sumitted others dependent writes without the sync flag set. This causes excessive anticipation/idling in the IO scheduler because sync and async writes get interleaved, causing a big performance regression for the below test case (which is meant to simulate sqlite like behaviour). ---- test case ---- int main(int argc, char **argv) { int fdes, i; FILE *fp; struct timeval start; struct timeval end; struct timeval res; gettimeofday(&start, NULL); for (i=0; i

vfs: Don't call attach_nobh_buffers() with an empty list

2009-02-06T21:34:22+00:00

This is a modification of a patch by Bill Pemberton nobh_write_end() could call attach_nobh_buffers() with head == NULL. This would result in a trap when attach_nobh_buffers() attempted to access bh->b_this_page. This can be illustrated by running the writev01 testcase from LTP on jfs. This error was introduced by commit 5b41e74a "vfs: fix data leak in nobh_write_end()". That patch did not take into account that if PageMappedToDisk() is true upon entry to nobh_write_begin(), then no buffers will be allocated for the page. In that case, we won't have to worry about a failed write leaving unitialized data in the page. Of course, head != NULL implies !page_has_buffers(page), so no need to test both. Signed-off-by: Dave Kleikamp Cc: Bill Pemberton Cc: Dmitri Monakhov Signed-off-by: Linus Torvalds

[CVE-2009-0029] System call wrappers part 10

2009-01-14T13:15:22+00:00

Signed-off-by: Heiko Carstens

filesystem freeze: implement generic freeze feature

2009-01-10T00:54:42+00:00

The ioctls for the generic freeze feature are below. o Freeze the filesystem int ioctl(int fd, int FIFREEZE, arg) fd: The file descriptor of the mountpoint FIFREEZE: request code for the freeze arg: Ignored Return value: 0 if the operation succeeds. Otherwise, -1 o Unfreeze the filesystem int ioctl(int fd, int FITHAW, arg) fd: The file descriptor of the mountpoint FITHAW: request code for unfreeze arg: Ignored Return value: 0 if the operation succeeds. Otherwise, -1 Error number: If the filesystem has already been unfrozen, errno is set to EINVAL. [akpm@linux-foundation.org: fix CONFIG_BLOCK=n] Signed-off-by: Takashi Sato Signed-off-by: Masayuki Hamaguchi Cc: Cc: Cc: Christoph Hellwig Cc: Dave Kleikamp Cc: Dave Chinner Cc: Alasdair G Kergon Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds