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NFS: Prevent a deadlock in the new writeback code

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We have to unlock the nfs_page before we call nfs_end_page_writeback
to avoid races with functions that expect the page to be unlocked
when PG_locked and PG_writeback are not set.
The problem is that nfs_unlock_request also releases the nfs_page,
causing a deadlock if the release of the nfs_open_context
triggers an iput() while the PG_writeback flag is still set...

The solution is to separate the unlocking and release of the nfs_page,
so that we can do the former before nfs_end_page_writeback and the
latter after.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>
This commit is contained in:
Trond Myklebust 2012-05-09 14:30:35 -04:00
parent dc327ed4cd
commit 3aff4ebb95
3 changed files with 15 additions and 4 deletions
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12
fs/nfs/pagelist.c
View File

@ -128,10 +128,10 @@ nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
}
/**
* nfs_unlock_request - Unlock request and wake up sleepers.
* nfs_unlock_request_dont_release - Unlock request and wake up sleepers.
* @req:
*/
void nfs_unlock_request(struct nfs_page *req)
void nfs_unlock_request_dont_release(struct nfs_page *req)
{
if (!NFS_WBACK_BUSY(req)) {
printk(KERN_ERR "NFS: Invalid unlock attempted\n");
@ -141,6 +141,14 @@ void nfs_unlock_request(struct nfs_page *req)
clear_bit(PG_BUSY, &req->wb_flags);
smp_mb__after_clear_bit();
wake_up_bit(&req->wb_flags, PG_BUSY);
}
/**
* nfs_unlock_request - Unlock request and release the nfs_page
*/
void nfs_unlock_request(struct nfs_page *req)
{
nfs_unlock_request_dont_release(req);
nfs_release_request(req);
}

6
fs/nfs/write.c
View File

@ -628,8 +628,9 @@ static void nfs_write_completion(struct nfs_pgio_header *hdr)
remove_req:
nfs_inode_remove_request(req);
next:
nfs_unlock_request(req);
nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
nfs_release_request(req);
}
out:
hdr->release(hdr);
@ -1042,8 +1043,9 @@ static void nfs_redirty_request(struct nfs_page *req)
struct page *page = req->wb_page;
nfs_mark_request_dirty(req);
nfs_unlock_request(req);
nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
nfs_release_request(req);
}
static void nfs_async_write_error(struct list_head *head)

1
include/linux/nfs_page.h
View File

@ -96,6 +96,7 @@ extern bool nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
struct nfs_page *req);
extern int nfs_wait_on_request(struct nfs_page *);
extern void nfs_unlock_request(struct nfs_page *req);
extern void nfs_unlock_request_dont_release(struct nfs_page *req);
/*
* Lock the page of an asynchronous request without getting a new reference