5accdf82ba
vfs_check_frozen() tests are racy since the filesystem can be frozen just after the test is performed. Thus in write paths we can end up marking some pages or inodes dirty even though the file system is already frozen. This creates problems with flusher thread hanging on frozen filesystem. Another problem is that exclusion between ->page_mkwrite() and filesystem freezing has been handled by setting page dirty and then verifying s_frozen. This guaranteed that either the freezing code sees the faulted page, writes it, and writeprotects it again or we see s_frozen set and bail out of page fault. This works to protect from page being marked writeable while filesystem freezing is running but has an unpleasant artefact of leaving dirty (although unmodified and writeprotected) pages on frozen filesystem resulting in similar problems with flusher thread as the first problem. This patch aims at providing exclusion between write paths and filesystem freezing. We implement a writer-freeze read-write semaphore in the superblock. Actually, there are three such semaphores because of lock ranking reasons - one for page fault handlers (->page_mkwrite), one for all other writers, and one of internal filesystem purposes (used e.g. to track running transactions). Write paths which should block freezing (e.g. directory operations, ->aio_write(), ->page_mkwrite) hold reader side of the semaphore. Code freezing the filesystem takes the writer side. Only that we don't really want to bounce cachelines of the semaphores between CPUs for each write happening. So we implement the reader side of the semaphore as a per-cpu counter and the writer side is implemented using s_writers.frozen superblock field. [AV: microoptimize sb_start_write(); we want it fast in normal case] BugLink: https://bugs.launchpad.net/bugs/897421 Tested-by: Kamal Mostafa <kamal@canonical.com> Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com> Tested-by: Dann Frazier <dann.frazier@canonical.com> Tested-by: Massimo Morana <massimo.morana@canonical.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
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| acpi | ||
| asm-generic | ||
| crypto | ||
| drm | ||
| keys | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| mtd | ||
| net | ||
| pcmcia | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| target | ||
| trace | ||
| video | ||
| xen | ||
| Kbuild | ||