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Fix a deadlock in the FreeBSD getpages VOP
FreeBSD has a per-page "busy" lock which is held when handling a page fault on a mapped file. This lock is also acquired when copying data from the DMU to the page cache in zfs_write(). File range locks are also acquired in both of these paths, in the opposite order with respect to the busy lock. In the getpages VOP, the range lock is only used to determine the extent of optional read-ahead and read-behind operations. To resolve the lock order reversal, modify the getpages VOP to avoid blocking on the range lock. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Ryan Moeller <ryan@ixsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #10519
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@ -4809,9 +4809,20 @@ zfs_getpages(struct vnode *vp, vm_page_t *ma, int count, int *rbehind,
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*/
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for (;;) {
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blksz = zp->z_blksz;
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lr = zfs_rangelock_enter(&zp->z_rangelock,
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lr = zfs_rangelock_tryenter(&zp->z_rangelock,
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rounddown(start, blksz),
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roundup(end, blksz) - rounddown(start, blksz), RL_READER);
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if (lr == NULL) {
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if (rahead != NULL) {
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*rahead = 0;
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rahead = NULL;
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}
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if (rbehind != NULL) {
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*rbehind = 0;
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rbehind = NULL;
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}
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break;
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}
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if (blksz == zp->z_blksz)
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break;
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zfs_rangelock_exit(lr);
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